GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 15 Dec 2018, 04:19

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

## Events & Promotions

###### Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Free GMAT Strategy Webinar

December 15, 2018

December 15, 2018

07:00 AM PST

09:00 AM PST

Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.
• ### $450 Tuition Credit & Official CAT Packs FREE December 15, 2018 December 15, 2018 10:00 PM PST 11:00 PM PST Get the complete Official GMAT Exam Pack collection worth$100 with the 3 Month Pack ($299) # Math Revolution Approach (DS)  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics Author Message Intern Joined: 26 Nov 2016 Posts: 6 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 07 Dec 2016, 23:17 MathRevolution wrote: At least 10 cars have tinting window and fog light. 40% cars which have tinting windows also have fog light, is the number of the cars with tinting windows larger than that of the cars with the fog light? 1) 80% cars which have fog light also have tinting windows 2) 52 cars have tinting windows or fog light or both ANS: If we were to solve this question with our trick, we should observe if one of conditions include ratio. If one of conditions contains ratio, then the condition with ratio has 90% of chance to become the answer. Since the condition 1) has ratio, the correct answer is A. Can you please explain the solution in detail Sent from my C6902 using GMAT Club Forum mobile app Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 08 Dec 2016, 00:38 a, b, c, d, and e are integers. Is the median of the integers greater than the average (arithmetic mean) of the integers? 1) a<b<c<d<e 2) b-a=e-d ==> In the original condition, there are 5 variables, so E is most likely to be the answer. By solving con 1) & con 2), you get (a,b,c,d,e)=(1,2,3,4,5), hence it is no, and you get (a,b,c,d,e)=(1,2,101,102,103), hence it is yes, so it is not sufficient. Therefore, the answer is E. Answer: E _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

09 Dec 2016, 00:44
Is x<y<z?

1) x-2<y-1<z
2) x+2<y+1<z

==> In the original condition, there are 3 variables (x, y, z), so E is most likely to be the answer.
By solving con 1) & con 2), you get 2x<2y<2z. From x<y<z, it is always yes, hence it is sufficient.
However, if you look at con 2), from x+1<x+2<y+1<z<z+1, you get x+1<y+1<z+1, and x<y<z, so it is always yes, hence it is sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 10 Dec 2016, 18:32 Hemanth2017 wrote: MathRevolution wrote: At least 10 cars have tinting window and fog light. 40% cars which have tinting windows also have fog light, is the number of the cars with tinting windows larger than that of the cars with the fog light? 1) 80% cars which have fog light also have tinting windows 2) 52 cars have tinting windows or fog light or both ANS: If we were to solve this question with our trick, we should observe if one of conditions include ratio. If one of conditions contains ratio, then the condition with ratio has 90% of chance to become the answer. Since the condition 1) has ratio, the correct answer is A. Can you please explain the solution in detail Sent from my C6902 using GMAT Club Forum mobile app Hi Hemanth2017, In general, one con is % and if one con is number, % is likely to be an answer. When it comes to 1), amongst cars with tinting windows, 40% of them have fog light. For the same cars with fog light, 80% have tinting windows. For instance, cars with only tinting window - six cars, both tinting window and fog light - four cars, only fog light - one car, which is 10>5 and yes. Hence, the answer is A. Happy Studying! _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

12 Dec 2016, 00:12
If the ratio of a to b to c to d is 1 to 2 to 3 to 4, what is the range of a, b, c and d?

1) The average (arithmetic mean) of b and d is 9
2) The sum of a and d is 15

==> If you modify the original condition and the question and look at the question again, from a=k, b=2k, c=3k, d=4k, there are 5 variables (a, b, c, d, k), and 4 equations. Therefore, D is most likely to be the answer. Con 1) = con 2), so k=3, and from range=d-a=4k-k=3k=3(3) = 9, it is sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 12 Dec 2016, 00:14 What is the standard deviation (d) of m, n, p? 1) m, n, and p are different 2) $$d^2-2d=0$$ ==> From the original condition, there are 3 variables, and therefore E is most likely to be the answer. By solving con 1) & con 2), from d(d-2)=0, you get d=0, 2. From con 1), m, n, and p are different and d≠0, it is always d=2 only, so it is unique and sufficient. Therefore, the answer is C. Answer: C _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

14 Dec 2016, 00:27
What is the median of 5 numbers?

1) Each of the 3 numbers is 11
2) The 2 greatest numbers of them are 21 and 25

==> If you modify the original condition and the question, the median of 5 numbers become the third number.
In case of con 1), from 11,11,11,( ),( ) or ( ),11,11,11,( ) or ( ), ( ),11,11,11, it is always median=11, so it is unique and sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 15 Dec 2016, 00:12 If x≠0, |x|/x=? 1) x<0 2) x=-1 ==> If you modify the original condition and the question, you get |x|=-x (x<0). Thus, if x<0, you get |x|/x=-x/x=-1, so con 1) = con 2), and therefore the answer is D. Answer: D _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

15 Dec 2016, 23:37
If the average (arithmetic mean) of 3 integers a, b, and c is 5, what is the value of a?

1) b=7
2) b=1-c

==> If you modify the original condition and the question and look at the question again, from a+b+c=15, you get a=15-(b+c), so you only need to know b+c. From con 2), you get b+c=1, so from a=15-(b+c)=15-1=14, it is unique and sufficient. Therefore, the answer is B. This question is related to mistake type 4(A).

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 18 Dec 2016, 17:18 If x and y are prime numbers, what is the smallest prime factor of $$xy^3$$ ? 1) x=even 2) x+y=odd ==> In the original condition, there are only 2 variables (x, y), hence C is most likely to be the answer. For con 1), if x=even, an even number that is also a prime number is only “2”, so the smallest prime factor of $$xy^3$$ becomes 2, and hence it is sufficient. For con 2), in order to get x+y=odd, since it is even+odd=odd, x or y always becomes “2”, so the smallest prime factor of $$xy^3$$ becomes “2”, and hence it is also sufficient. This question is also related to mistake type 4(B), where con 1) is easy and con 2) is difficult. This type of question is a 5051-level question. The answer is D. Answer: D _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

18 Dec 2016, 17:23
If $$a^3b^4c^5<0$$, is $$ab^2<0$$?

1) a<0
2) c>0

==> If you modify the original condition and the question and look at the question again, from If $$a^3b^4c^5<0$$, there are only odd variables, so you get If ac<0. Then, the que is $$ab^2<0$$? becomes a<0?, and hence con 1) is yes and sufficient. Also, from ac<0, you get c>0?, and hence con 2) is yes and sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 21 Dec 2016, 00:43 If ab=c, b=? 1) c≠0 2) |a-c|≤0 ==> In the original condition, there are 3 variables (a, b, c) and 1 equation (ab=c). In order to match the number of variables to the number of equations, there must be 2 equations, and therefore C is most likely to be the answer. By solving con 1) and con 2), from con 2), you get a=c, and if you substitute this into ab=x, you get ab=a. In order to divide a from both sides, it needs to be a≠0. From con 1), it is c=a≠0, and if you divide both sides by a, you get b=1, hence it is unique and sufficient. Therefore, the answer is C. Answer: C _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

23 Dec 2016, 01:27
If x, y and z are different integers, what is the value of y?

1) The average (arithmetic mean) of x, y and z is 2
2) x<y<z

==> In the original condition, there are 3 variables (x, y, z), and in order to match the number of variables to the number of equations, there must be 3 equations, and therefore E is most likely to be the answer. By solving con 1) & con 2), you get (x+y+z)/3=2. Since it is x<y<z, you always get median=average=y=2. Hence it is unique and sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 25 Dec 2016, 17:34 If r and s are positive integers, is r+s an odd number? 1) r and s are consecutive 2) r=s+1 ==> In the original condition, there are 2 variables (r, s), and therefore C is most likely to be the answer. By solving con 1) & con 2), you get con 1) = con 2), so it becomes r+s=s+1+s=2s+1=odd, and hence it is yes and sufficient. Therefore, the answer is D. This is a 5051-level question related to mistake type 4(B). Answer: D _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
If x and y are positive integers, xy-2=?  [#permalink]

### Show Tags

25 Dec 2016, 17:37
If x and y are positive integers, $$x^y^-^2$$=?
1) $$x^2=1$$
2) $$y^2=4$$

==> In the original condition, there are 2 variables (x), and in order to match the number of variables to the number of equations, there must be 2 equations, and therefore C is most likely to be the answer. By solving con 1) & con 2), you get x=-1, 1 and y=-2, 2. Since x and y are positive integers, only x=1 and y=2 are possible, and con 1) becomes $$1^y^-^2=x^2^-^2=x^0=1$$.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 31 Dec 2016, 00:43 If a and b are integers, is ab an odd? 1) a=0 2) b=1-a ==> In the original condition, there are 2 variables (a, b), and therefore C is most likely to be the answer. By solving con 1) and con 2), from a=0 and b=1, you get ab0*1=0=even, hence no, it is sufficient. Therefore, C is the answer. However, this is an integer question, one of the key questions. Thus, if you apply CMT 4 (A, B), if 1) a=0, you get ab=0 and it is always even, hence no, it is sufficient. Also, for con 2), from a+b=1=odd, and (a, b)=(odd, even), (even, odd), you get ab=even, hence yes, it is sufficient. Therefore, the answer is D. This question is related to CMT 4(B). In other words, con 1) is easy and con 2) is difficult, so you apply CMT 4(B) (If you get A and B easily, consider B). Answer: D _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

31 Dec 2016, 00:48
Is n an even number?

1) n(n+1)/2 is an even number
2) n(n+2) is an even number

==> In the original condition, there is 1 variable (n), and therefore D is most likely to be the answer.
However, for con 1), you get n=3 no, n=8 yes, and hence it is not sufficient, and for con 2), in order to get n(n+2)=even, you need to get n=even, and hence yes, it is sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 31 Dec 2016, 00:49 Is 1/a>1/b? 1) a<b 2) a<b<0 ==> If you modify the original condition and the question and check the question again, you get a<b<0--> 1/a>1/b. In other words, it does not become a<b --> 1/a>1/b. Therefore, B is the answer. Answer: B _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6639
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

### Show Tags

01 Jan 2017, 17:38
If ab=0, is |a-b|>0?
1) a=0
2) b<0

==> If you modify the original condition and the question, you get is a≠b? Also, there are 2 variables (a, b) and 1 equation (ab=0), in order to match the number of variables to the number of equations, there must be 1 equation as well, and therefore D is most likely to be the answer.
For con 1), you get a=b=0 no a=0 and b=3, hence yes, it is not sufficient.
For con 2), you get b<0 and a=0, hence yes, it is sufficient.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Math Revolution Approach (DS) [#permalink] ### Show Tags 01 Jan 2017, 17:40 If m and n are positive integers, is $$10^n$$+m divisible by 3? 1) n=1 2) m=2 ==> If you modify the original condition and the question, “Is $$10^n$$+m=3t? (t=any positive integer)” is equal to “Is the sum of all the digits of $$10^n$$+m divisible by 3?” Then, as from con 2), if you know m=2, from $$10^n$$+2 => 12, 102, 1002…., the sum of the digits always become 3, which is divisible by 3, and hence yes, it is sufficient. Therefore, the answer is B. Answer: B _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Re: Math Revolution Approach (DS) &nbs [#permalink] 01 Jan 2017, 17:40

Go to page   Previous    1  ...  3   4   5   6   7   8   9   10   11  ...  29    Next  [ 572 posts ]

Display posts from previous: Sort by

# Math Revolution Approach (DS)

Moderator: souvonik2k

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.