Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 39702

New DS set!!! [#permalink]
Show Tags
10 Apr 2013, 08:10
19
This post received KUDOS
Expert's post
103
This post was BOOKMARKED
The next set of medium/hard DS questions. I'll post OA's with detailed explanations after some discussion. Please, post your solutions along with the answers.1. What is the product of three consecutive integers?(1) At least one of the integers is positive (2) The sum of the integers is less than 6 Solution: newdsset15065360.html#p12119022. If x and y are both positive integers and x>y, what the remainder when x is divided by y?(1) y is a twodigit prime number (2) x=qy+9, for some positive integer q Solution: newdsset15065360.html#p12119033. The length of the median BD in triangle ABC is 12 centimeters, what is the length of side AC?(1) ABC is an isosceles triangle (2) AC^2 = AB^2 + BC^2 Solution: newdsset15065360.html#p12119044. Two machines, A and B, each working at a constant rate, can complete a certain task working together in 6 days. In how many days, working alone, can machine A complete the task?(1) The average time A and B can complete the task working alone is 12.5 days. (2) It would take machine A 5 more days to complete the task alone than it would take for machine B to complete the task Solution: newdsset15065360.html#p12119065. Set A={32x, 3x, 3, 3+x, 3+2x}, where x is an integer. Is the standard deviation of set A more than the standard deviation of set B={32x, 3x, 3, 3+x, 3+2x, y}(1) The standard deviation of set A is positive (2) y=3 Solution: newdsset15065360.html#p12119076. The ratio of the number of employees of three companies X, Y and Z is 3:4:8, respectively. Is the average age of all employees in these companies less than 40 years?(1) The total age of all the employees in these companies is 600 (2) The average age of employees in X, Y, and Z, is 40, 20, and 50, respectively. Solution: newdsset15065380.html#p12119087. Was the average (arithmetic mean) temperature in city A in March less than the average (arithmetic mean) temperature in city B in March?(1) The median temperature in City A in March was less than the median temperature in city B (2) The ratio of the average temperatures in A and B in March was 3 to 4, respectively Solution: newdsset15065380.html#p12119098. Two marbles are drawn from a jar with 10 marbles. If all marbles are either red of blue, is the probability that both marbles selected will be red greater than 3/5?(1) The probability that both marbles selected will be blue is less than 1/10 (2) At least 60% of the marbles in the jar are red Solution: newdsset15065380.html#p12119109. If x is an integer, is x^2>2x?(1) x is a prime number. (2) x^2 is a multiple of 9. Solution: newdsset15065380.html#p121191110. What is the value of the media of set A?(1) No number in set A is less than the average (arithmetic mean) of set A. (2) The average (arithmetic mean) of set A is equal to the range of set A. Solution: newdsset15065380.html#p1211912Kudos points for each correct solution!!!
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 01:27
manishuol wrote: okay ..sir .. as you said in the first line of ur solution to this Q ...
Given that the ratio of the number of employees is 3x:4x:8x, for some positive multiple x.,, I think you have taken x as an integer so that it is flexible to say tat this ratio can be 3:4:8 or 3*2 : 4*2 : 8*2 or 6:8:16 or 9:12:24... I would like to know why can't we change this ratio of number employees to the ratio of weights of employees of the three companies...Can we change the Ratio of number of Employees to the Ratio of weights of Employees of three companies .... Pls Advise , Thanks in Advance !! What is the ratio of weights? Anyway, we need to find whether (average age)=(total age)/(# of employees)<40, or whether (total age)/(3x+4x+8x)<40, which is the same as: is (total age)<600x? Does this makes sense?
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Status: Pushing Hard
Affiliations: GNGO2, SSCRB
Joined: 30 Sep 2012
Posts: 89
Location: India
Concentration: Finance, Entrepreneurship
GPA: 3.33
WE: Analyst (Health Care)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 02:08
Bunuel wrote: manishuol wrote: okay ..sir .. as you said in the first line of ur solution to this Q ...
Given that the ratio of the number of employees is 3x:4x:8x, for some positive multiple x.,, I think you have taken x as an integer so that it is flexible to say tat this ratio can be 3:4:8 or 3*2 : 4*2 : 8*2 or 6:8:16 or 9:12:24... I would like to know why can't we change this ratio of number employees to the ratio of weights of employees of the three companies...Can we change the Ratio of number of Employees to the Ratio of weights of Employees of three companies .... Pls Advise , Thanks in Advance !! What is the ratio of weights? Anyway, we need to find whether (average age)=(total age)/(# of employees)<40, or whether (total age)/(3x+4x+8x)<40, which is the same as: is (total age)<600x? Does this makes sense?  I think there is some communication gap b/w us but still sir will try to make u understand what am I trying to say otherwise I will concentrate on ur solution & will try to understand.... First Ratio of # of Employees given as :::::: 3:4:8 ... so for me the # of employees in the three companies can be 3,4,8 or 6,8,16 or 9,12,24 any three numbers that satisfy the ratio 3:4:8. okay. Second, in company X there must some average weight of employees, right ?? lets say that average weight is a1 okay. so the total weight of employees in company X will be 3*a1 , if we take that there 3 employees in company X. or if u want you can take this as 6 but for that u must satisfy the ratio of # of employees accordingly okay. now similarly, in company Y there must be some average weight of employees, right ?? lets say that average weight is a2 okay. & therefore the total weight of employees in company Y will be 4*a2. now similarly, in company Z there must some average weight of employees, right ?? lets say that average weight is a3 okay. & therefore the total weight of employees in company Z will be 8*a3. Now the total weight of employees in three companies will be 3*a1 + 4*a2 + 8*a3......... okay. & if we are taking number of employees as 6,8,16, this will become 3*2*a1 + 4*2*a2 + 8*2*a3.... & in both the cases the # of employees will change but not the equation as if we take in first case total weight of employees in three companies is 3*a1 + 4*a2 + 8*a3 so in this case the average weight will be 3*a1 + 4*a2 + 8*a3/3+4+8 ... or 3a1+4a2+8a3/15 & as the Q asks (average age)=(total age)/(# of employees)<40, or whether 3a1+4a2+8a3/15<40, or 3a1+4a2+8a3<15*40 or 3a1+4a2+8a3<600. similarly for second scenario, if we take #of employees as 6,8,16 maintaining the same ratio of employees as 3:4:8. in this case the total weight will be 3*2*a1 + 4*2*a2 + 8*2*a3 or 6a1+8a2+16a3 & the average will be 6a1+8a2+16a3/6+8+16 or 6a1+8a2+16a3/30 again as the Q asks is (average age)=(total age)/(# of employees)<40, or whether 6a1+8a2+16a3/30, or 6a1+8a2+16a3<30*40 or 6a1+8a2+16a3<1200 or 2 (3a1+4a2+8a3) < 2*600 or 3a1+4a2+8a3<600 .. but both the statements are disallowing it. so that's how I have this solution. if you think this can't be the way, so I'm really sorry to waste your time. As you are the Master of GMAT Math & you can't be wrong, I will review my logic again & concentrate on your solution to understand it better. Thanks for your precious time . Thanks !!!!
_________________
If you don’t make mistakes, you’re not working hard. And Now that’s a Huge mistake.



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 03:55
manishuol wrote: Bunuel wrote: manishuol wrote: okay ..sir .. as you said in the first line of ur solution to this Q ...
Given that the ratio of the number of employees is 3x:4x:8x, for some positive multiple x.,, I think you have taken x as an integer so that it is flexible to say tat this ratio can be 3:4:8 or 3*2 : 4*2 : 8*2 or 6:8:16 or 9:12:24... I would like to know why can't we change this ratio of number employees to the ratio of weights of employees of the three companies...Can we change the Ratio of number of Employees to the Ratio of weights of Employees of three companies .... Pls Advise , Thanks in Advance !! What is the ratio of weights? Anyway, we need to find whether (average age)=(total age)/(# of employees)<40, or whether (total age)/(3x+4x+8x)<40, which is the same as: is (total age)<600x? Does this makes sense?  I think there is some communication gap b/w us but still sir will try to make u understand what am I trying to say otherwise I will concentrate on ur solution & will try to understand.... Second, in company X there must some average weight of employees, right ?? lets say that average weight is a1 okay. Yes, your solution is not correct. Also, we have the number of employees and age. What is weight???
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Status: Pushing Hard
Affiliations: GNGO2, SSCRB
Joined: 30 Sep 2012
Posts: 89
Location: India
Concentration: Finance, Entrepreneurship
GPA: 3.33
WE: Analyst (Health Care)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 04:06
Sorry, I have made a mistake to write weight instead of age. Anyways. Thanks for clearing my Doubts. Now, I realize, I was wrong & now will concentrate on ur solution....... I appreciate your help. Thanks a Lot Big Brother !!!!! Cheers .....
_________________
If you don’t make mistakes, you’re not working hard. And Now that’s a Huge mistake.



Director
Joined: 25 Apr 2012
Posts: 728
Location: India
GPA: 3.21
WE: Business Development (Other)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 06:20
1. What is the product of three consecutive integers? (1) At least one of the integers is positive (2) The sum of the integers is less than 6 Sol:Consider St 1, we get atleast one of the integer is positive ie. may be more than 1 integer are also postive. Looking at possible option based on statement we have Case 1: + Possible options : 2,1 and 0 ( But Zero is neither positive nor negative so we can rule out this option) Case 2: ++ Possible options: 1,0,1 (again 0 is neither postive nor negative and hence cannot be the option) Case 3 :+++ 1,2,3 or 3,4,5 Product can be anything and hence not sufficient St 2: The sum of the integers is less than 6 Possible options Case 1:1,0,1 Case 2: 0,1,2 Case 3: 3,2,1 Again more than 1 answer is possible Combining we get Sum< 6 and Atleast one integer is positve and hence Case 3 from St1 can be removed But Case 3 of statement 2 is still valid and hence we can get 2 answers. Ans should be E
_________________
“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 06:24
mridulparashar1 wrote: 1. What is the product of three consecutive integers?
(1) At least one of the integers is positive (2) The sum of the integers is less than 6
Sol:Consider St 1, we get atleast one of the integer is positive ie. may be more than 1 integer are also postive.
Looking at possible option based on statement we have
Case 1: + Possible options : 2,1 and 0 ( But Zero is neither positive nor negative so we can rule out this option) Case 2: ++ Possible options: 1,0,1 (again 0 is neither postive nor negative and hence cannot be the option) Case 3 :+++ 1,2,3 or 3,4,5 Product can be anything and hence not sufficient
St 2: The sum of the integers is less than 6 Possible options
Case 1:1,0,1 Case 2: 0,1,2 Case 3: 3,2,1
Again more than 1 answer is possible
Combining we get Sum< 6 and Atleast one integer is positve and hence Case 3 from St1 can be removed
But Case 3 of statement 2 is still valid and hence we can get 2 answers.
Ans should be E There is no positive integer in case 3 (red). Check correct solution here: newdsset15065360.html#p1211902Hope it helps.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Director
Joined: 25 Apr 2012
Posts: 728
Location: India
GPA: 3.21
WE: Business Development (Other)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 06:32
2. If x and y are both positive integers and x>y, what the remainder when x is divided by y? (1) y is a twodigit prime number (2) x=qy+9, for some positive integer q Sol: From St1, we get that x/y will be of the form x/y= x/11, x/13, x/17, x/29, x/37...... Consider x = 12, Y =11, remainder 1 Consider x= 13, Y =11, remainder 2 So we have 2 ans and hence St 1 not sufficent alone (A & D ruled out) St 2 x=qy+9, for some positive integer q x/y= q+ 9/y > remainder will depend on value of y and hence st 2 not sufficient alone (Option B ruled out) Combining both statement we get that remainder will always be 9 since Y is a 2 digit prime no Hence answer should be C
_________________
“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”



Director
Joined: 25 Apr 2012
Posts: 728
Location: India
GPA: 3.21
WE: Business Development (Other)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 06:49
5. Set A={32x, 3x, 3, 3+x, 3+2x}, where x is an integer. Is the standard deviation of set A more than the standard deviation of set B={32x, 3x, 3, 3+x, 3+2x, y} (1) The standard deviation of set A is positive (2) y=3 Sol: We know SD >/ 0 and hence Set A is Positive does not tell us about y in statement B So St 1 is alone not sufficent St 2: y =3 Set A : SD \sqrt{10X^2/5} Set B : SD is \sqrt{10x^2/6} Since x is an integer we have SD of A as x \sqrt{2} and SD of B as x\sqrt{5/3} Clearly SD of A is greater than that of B and hence ans should be B
_________________
“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”



Director
Joined: 25 Apr 2012
Posts: 728
Location: India
GPA: 3.21
WE: Business Development (Other)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 06:59
6. The ratio of the number of employees of three companies X, Y and Z is 3:4:8, respectively. Is the average age of all employees in these companies less than 40 years? (1) The total age of all the employees in these companies is 600 (2) The average age of employees in X, Y, and Z, is 40, 20, and 50, respectively. Sol: From St 1 we have 600 = Average age of all employees (A)* No. of Employees(n) So Q asks is A<40 Clearly 1 alone is not sufficient St 2 : Let the employees in the company be in the ratio 3c :4c: 8c where c is a positive integer Therefore we have (3c*40+4c*20+ 5c* 50 )/15c = A If c =1 we have (120+80+250)/15 > (450/15) = 30 < 40 If c =2 we have ( 3*2*40+ 4*2*20+ 5*2*50/15*2), A = 900/30 < 40 If c= 3, we have (360+240+750)/45 > 1350/45 < 40 If c= 4, we have ( 480+320+1000)/60 > 1800/60 < 40 Therefore ans should be B
_________________
“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”



Manager
Status: Breaking my head!!
Joined: 27 Jan 2013
Posts: 71
Location: India
Concentration: General Management, Operations
GPA: 3.51
WE: Other (Transportation)

Re: New DS set!!! [#permalink]
Show Tags
15 Apr 2013, 10:21
Bunuel wrote: 3. The length of the median BD in triangle ABC is 12 centimeters, what is the length of side AC?
(1) ABC is an isosceles triangle. Clearly insufficient.
(2) AC^2 = AB^2 + BC^2. This statement implies that ABC is a right triangle and AC is its hypotenuse. Important property: median from right angle is half of the hypotenuse, hence BD=12=AC/2, from which we have that AC=24. Sufficient.
Answer: B. Hi Bunnel Could you elaborate how this is true  median from right angle is half of the hypotenuse?? Thanks



Intern
Joined: 02 Sep 2012
Posts: 27
Location: India
WE: Supply Chain Management (Retail)

Re: New DS set!!! [#permalink]
Show Tags
18 Apr 2013, 10:02
Hi Bunuel.. How to be sure that A={0,0,0,0} and A={1,2,2,3} are the only sets possible from Statement2. Is there any quick method to find this. infact i was unable to find A={1,2,2,3}. Bunuel wrote: 10. What is the value of the media of set A?
(1) No number in set A is less than the average (arithmetic mean) of set A.
Since no number is less than the average, then no number is more than the average, which implies that the list contains identical elements: A={x, x, x, ...}. From this it follows that (the average)=(the median). But we don't know the value of x, thus this statement is NOT sufficient.
(2) The average (arithmetic mean) of set A is equal to the range of set A.
Not sufficient: if A={0, 0, 0, 0}, then (the median)=0, but if A={1, 2, 2, 3}, then (the median)=2.
(1)+(2) From (1) we have that the list contains identical elements. The range of all such sets is 0. Therefore, from (2) we have that (the average)=(the range)=0 and since from (1) we also know that (the average)=(the median), then (the median)=0. Sufficient.
Answer: C.



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
19 Apr 2013, 03:59
buffaloboy wrote: Hi Bunuel.. How to be sure that A={0,0,0,0} and A={1,2,2,3} are the only sets possible from Statement2. Is there any quick method to find this. infact i was unable to find A={1,2,2,3}. Bunuel wrote: 10. What is the value of the media of set A?
(1) No number in set A is less than the average (arithmetic mean) of set A.
Since no number is less than the average, then no number is more than the average, which implies that the list contains identical elements: A={x, x, x, ...}. From this it follows that (the average)=(the median). But we don't know the value of x, thus this statement is NOT sufficient.
(2) The average (arithmetic mean) of set A is equal to the range of set A.
Not sufficient: if A={0, 0, 0, 0}, then (the median)=0, but if A={1, 2, 2, 3}, then (the median)=2.
(1)+(2) From (1) we have that the list contains identical elements. The range of all such sets is 0. Therefore, from (2) we have that (the average)=(the range)=0 and since from (1) we also know that (the average)=(the median), then (the median)=0. Sufficient.
Answer: C. A={0, 0, 0, 0} and A={1, 2, 2, 3} are NOT the only sets possible. For example A={0, 0, 0} and A={1, 2, 3}. You can find these sets by trial and error.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 24 May 2013
Posts: 20
Location: United Kingdom
WE: Project Management (Real Estate)

Re: New DS set!!! [#permalink]
Show Tags
31 May 2013, 09:24
4. Two machines, A and B, each working at a constant rate, can complete a certain task working together in 6 days. In how many days, working alone, can machine A complete the task? (1) The average time A and B can complete the task working alone is 12.5 days. (2) It would take machine A 5 more days to complete the task alone than it would take for machine B to complete the task Ans B , Given : Ta + Tb = 6 ( time for working together is 6 days) Please explain if wrong Explanation as 1 As avg value given for individual working rate, (we want specific value for Ra) , as Ra can take multiple values in this case, stmt not sufficient. 2. Ta= Tb +5 & Ta + Tb =6 given in main stmt therefore Ans B Please correct if wrong
_________________
Correct me If I'm wrong !! looking for valuable inputs



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
09 Jul 2013, 00:34



Manager
Joined: 06 Feb 2010
Posts: 173
Concentration: Marketing, Leadership
Schools: University of Dhaka  Class of 2010
GPA: 3.63
WE: Business Development (Consumer Products)

Re: New DS set!!! [#permalink]
Show Tags
26 Nov 2013, 02:36
Bunuel wrote: 3. The length of the median BD in triangle ABC is 12 centimeters, what is the length of side AC?
(1) ABC is an isosceles triangle. Clearly insufficient.
(2) AC^2 = AB^2 + BC^2. This statement implies that ABC is a right triangle and AC is its hypotenuse. Important property: median from right angle is half of the hypotenuse, hence BD=12=AC/2, from which we have that AC=24. Sufficient.
Answer: B. if ABC is isosceles triangle then all sides are equal. so AC=24. why not?
_________________
Practice Makes a Man Perfect. Practice. Practice. Practice......Perfectly
Critical Reasoning: http://gmatclub.com/forum/bestcriticalreasoningshortcutsnotestips91280.html
Collections of MGMAT CAT: http://gmatclub.com/forum/collectionsofmgmatcatmath152750.html
MGMAT SC SUMMARY: http://gmatclub.com/forum/mgmatscsummaryoffourthedition152753.html
Sentence Correction: http://gmatclub.com/forum/sentencecorrectionstrategiesandnotes91218.html
Arithmatic & Algebra: http://gmatclub.com/forum/arithmaticalgebra93678.html
Helpful Geometry formula sheet: http://gmatclub.com/forum/bestgeometry93676.html
I hope these will help to understand the basic concepts & strategies. Please Click ON KUDOS Button.



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
26 Nov 2013, 02:46
monirjewel wrote: Bunuel wrote: 3. The length of the median BD in triangle ABC is 12 centimeters, what is the length of side AC?
(1) ABC is an isosceles triangle. Clearly insufficient.
(2) AC^2 = AB^2 + BC^2. This statement implies that ABC is a right triangle and AC is its hypotenuse. Important property: median from right angle is half of the hypotenuse, hence BD=12=AC/2, from which we have that AC=24. Sufficient.
Answer: B. if ABC is isosceles triangle then all sides are equal. so AC=24. why not? (1) says that ABC is an isosceles triangle, not equilateral. Also, if ABC were equilateral AC would be \(\frac{24}{\sqrt{3}}\) not 24. Hope it's clear.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 31 Aug 2011
Posts: 215

Re: New DS set!!! [#permalink]
Show Tags
23 Dec 2013, 22:42
4. Two machines, A and B, each working at a constant rate, can complete a certain task working together in 6 days. In how many days, working alone, can machine A complete the task? Given that 1/A+1/B=1/6, where A is the time needed for machine A to complete the task working alone and B is the time needed for machine B to complete the task working alone. Can anyone please explain how 1/A + 1/B = 1/6
_________________
If you found my contribution helpful, please click the +1 Kudos button on the left, I kinda need some =)



Math Expert
Joined: 02 Sep 2009
Posts: 39702

Re: New DS set!!! [#permalink]
Show Tags
24 Dec 2013, 02:27
PUNEETSCHDV wrote: 4. Two machines, A and B, each working at a constant rate, can complete a certain task working together in 6 days. In how many days, working alone, can machine A complete the task?
Given that 1/A+1/B=1/6, where A is the time needed for machine A to complete the task working alone and B is the time needed for machine B to complete the task working alone.
Can anyone please explain how 1/A + 1/B = 1/6 Two machines, A and B, each working at a constant rate, can complete a certain task working together in 6 days. In how many days, working alone, can machine A complete the task?A is the time needed for machine A to complete the task working alone, thus the rate of A is 1/A job/day. B is the time needed for machine B to complete the task working alone, thus the rate of A is 1/B job/day. Their combined rate is 1/A+1/B, which given to be equal to 1/6. Hope this helps.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 05 Nov 2012
Posts: 170

Re: New DS set!!! [#permalink]
Show Tags
26 Dec 2013, 15:14
Bunuel wrote: 2. If x and y are both positive integers and x>y, what the remainder when x is divided by y?
If \(x\) and \(y\) are positive integers, there exist unique integers \(q\) and \(r\), called the quotient and remainder, respectively, such that \(y =divisor*quotient+remainder= xq + r\) and \(0\leq{r}<x\).
(1) y is a twodigit prime number. Clearly insufficient since we know nothinf about x.
(2) x=qy+9, for some positive integer q. It's tempting to say that this statement is sufficient and \(r=9\), since given equation is very similar to \(y =divisor*quotient+remainder= xq + r\) . But we don't know whether \(y>9\): remainder must be less than divisor.
For example: If \(x=10\) and \(y=1\) then \(10=1*1+9\), then the remainder upon division 10 by 1 is zero. If \(x=11\) and \(y=2\) then \(11=1*2+9\), then the remainder upon division 11 by 2 is one. Not sufficient.
(1)+(2) From (2) we have that \(x=qy+9\) and from (1) that y is more than 9 (since it's a twodigit number), so we have direct formula of remainder, as given above. Sufficient.
Answer: C. Hello Bunuel, the questions says x is divided by y.... So x will be dividend and y will be divisor.... the very first representation between y and x will confuse a better understanding of the latter explanation. Why don't you switch x and y in the first formula too Thank you.



Intern
Joined: 12 Jul 2013
Posts: 12
Concentration: Economics, Finance
GPA: 3.46

Re: New DS set!!! [#permalink]
Show Tags
07 Jan 2014, 06:47
Bunuel wrote: 10. What is the value of the media of set A?
(1) No number in set A is less than the average (arithmetic mean) of set A.
Since no number is less than the average, then no number is more than the average, which implies that the list contains identical elements: A={x, x, x, ...}. From this it follows that (the average)=(the median). But we don't know the value of x, thus this statement is NOT sufficient.
(2) The average (arithmetic mean) of set A is equal to the range of set A.
Not sufficient: if A={0, 0, 0, 0}, then (the median)=0, but if A={1, 2, 2, 3}, then (the median)=2.
(1)+(2) From (1) we have that the list contains identical elements. The range of all such sets is 0. Therefore, from (2) we have that (the average)=(the range)=0 and since from (1) we also know that (the average)=(the median), then (the median)=0. Sufficient.
Answer: C.. Bununel, what if Set A only contains one factor "1"?
_________________
What does't kill you makes you stronger.







Go to page
Previous
1 2 3 4 5 6 7
Next
[ 139 posts ]




