Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 02 Jan 2011
Posts: 9

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 00:34
I am not so certain whether I am right but I would go with D in #9.
IF x<0 and y<0 then sqrt(x^2)/x=x/x, then x/x=1; because there is a minus in front of x, than (x) should be positive.
sqrt two negative y gives square root of y^2, than because y<1, y is negative as well. y.
From the expression we've got 1+y, thus D should be a correct answer.



Senior Manager
Joined: 23 Oct 2010
Posts: 358
Location: Azerbaijan
Concentration: Finance

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 00:51
Bunuel, could u please tell us which question is still unanswered or answered wrong by all of us? I want to think on such questions more, before u post solutions. and btw, do u read our solutions or just only answers? I wonder whether my way of thinking was ok. in some cases I tried to use another method not to repeat others. I just wonder whether it worked, or it was just coincidence
_________________
Happy are those who dream dreams and are ready to pay the price to make them come true
I am still on all gmat forums. msg me if you want to ask me smth



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 01:04



Intern
Joined: 02 Jan 2011
Posts: 9

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 01:43
Was it the wrong solution of #9. It seems to me that my post was removed



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 01:50



Senior Manager
Joined: 23 Oct 2010
Posts: 358
Location: Azerbaijan
Concentration: Finance

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 01:51
Bunuel wrote: As for your other question: I don't see a solution for #7, so you can try this one.
ok my answer to the q7 is D , because D is the leader of the day hehe kidding the answer is really D ,because 2/3(L+A+W) =F 3/7(F+W+A)=L 4/11(F+W+L)=A total=360 (I deleted the 0s just to make a number easy) W=? 2/3(L+A+W) =F means F=2/3(360F) =>(2/3)*360=5/3F=> F=144 3/7(F+W+A)=L means L=3/7(360L) => L=108 4/11(F+W+L)=A means A=4/11(360A)=>A=96 W=360 (L+A+F)=36014410896=12 or W=120 000 (return the 0s which were deleted before)
_________________
Happy are those who dream dreams and are ready to pay the price to make them come true
I am still on all gmat forums. msg me if you want to ask me smth



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8298
Location: Pune, India

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 02:44
utkarshlavania wrote: [quote2]9. If x and y are negative numbers, what is the value of \(\frac{\sqrt{x^2}}{x}\sqrt{y*y}\)? A. 1+y B. 1y C. 1y D. y1 E. xy
Correction/suggestion/advice/confirmation  needed Answer to 9th question If x and y are negative numbers, what is the value of \(\frac{\sqrt{x^2}}{x}\sqrt{y*y}\)?[/b] Sqrtx^2/xsqrt(y*y) = x/xy= 1y Responding to a pm: First of all, I would suggest you to put x = 2 and y = 3 and see what you get.
\(\frac{\sqrt{x^2}}{x}\sqrt{y*y}\)
\(\frac{\sqrt{(2)^2}}{2}\sqrt{(3)*3}\)
\(\frac{2}{2}\sqrt{9}\) (because square root will always be positive)
1  3 = 1 + y (since y = 3)
Coming to your solution:
I see you have everything correct till the last step: x/xy
x/x will be 1 which is fine. What about y? Do you remember how we define mods? We say: x = x if x >= 0 x = x if x < 0
Why? If x >= 0 e.g. say x = 5, x = x = 5 Instead, if x < 0 e.g. say x = 6, is x = x? No! mods are never negative. So x = x = (6) = 6 (Since x itself is negative, mod of x is negative of x which becomes positive.)
Therefore, if we know that y is negative, what is the value of y? y = y
Therefore, x/xy = 1 (y) = 1 + y
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
GMAT selfstudy has never been more personalized or more fun. Try ORION Free!



Intern
Joined: 03 Sep 2010
Posts: 15

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 05:36
@karishma
then why is x/x =1 , should not it be 1 as x=x and denominator is negative as well



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 05:59



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8298
Location: Pune, India

Re: Baker's Dozen
[#permalink]
Show Tags
11 Mar 2012, 20:52
utkarshlavania wrote: @karishma
then why is x/x =1 , should not it be 1 as x=x and denominator is negative as well You are right that x=x since x is negative but tell me, what is x, negative or positive? Negative of negative gives you positive, right? So x must be positive. Now, if x is negative, x/x must be positive/negative giving you 1. You are confusing yourself too much with negatives and positives. Just think of it this way: x/x = x/x (By definition, since x = x when x < 0) x/x = 1 ( x and x get canceled here leaving you with 1)
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
GMAT selfstudy has never been more personalized or more fun. Try ORION Free!



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:43
SOLUTIONS:1. A password on Mr. Wallace's briefcase consists of 5 digits. What is the probability that the password contains exactly three digit 6?A. 860/90,000 B. 810/100,000 C. 858/100,000 D. 860/100,000 E. 1530/100,000 Total # of 5 digit codes is 10^5, notice that it's not 9*10^4, since in a code we can have zero as the first digit. # of passwords with three digit 6 is \(9*9*C^3_5=810\): each out of two other digits (not 6) has 9 choices, thus we have 9*9 and \(C^3_5\) is ways to choose which 3 digits will be 6's out of 5 digits we have. \(P=\frac{favorable}{total}=\frac{810}{10^5}\) Answer: B.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  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: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:45



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:46



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:48



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:50



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:52
6. A pool has two water pumps A and B and one drain C. Pump A alone can fill the whole pool in x hours, and pump B alone can fill the whole pool in y hours. The drain can empty the whole pool in z hours, where z>x. With pumps A and B both running and the drain C unstopped till the pool is filled, which of the following represents the amount of water in terms of the fraction of the pool which pump A pumped into the pool?A. \(\frac{yz}{x+y+z}\) B. \(\frac{yz}{yz+xzxy}\) C. \(\frac{yz}{yz+xz+xy}\) D. \(\frac{xyz}{yz+xzxy}\) E. \(\frac{yz+xzxy}{yz}\) With pumps A and B both running and the drain unstopped the pool will be filled in a rate \(\frac{1}{x}+\frac{1}{y}\frac{1}{z}=\frac{yz+xzxy}{xyz}\) pool/hour. So, the pool will be filled in \(\frac{xyz}{yz+xzxy}\) hours (time is reciprocal of rate). In \(\frac{xyz}{yz+xzxy}\) hours A will pump \(\frac{1}{x}*\frac{xyz}{yz+xzxy}=\frac{yz}{yz+xzxy}\) amount of the water into the pool. Answer: B.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  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: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:56



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:57



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 03:59



Math Expert
Joined: 02 Sep 2009
Posts: 49493

Re: Baker's Dozen
[#permalink]
Show Tags
13 Mar 2012, 04:00




Re: Baker's Dozen &nbs
[#permalink]
13 Mar 2012, 04:00



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



