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

 It is currently 23 Oct 2019, 01:15 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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  Math Revolution Approach (DS)

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Math Revolution Approach (DS)  [#permalink]

Show Tags

x+y=?

ANS:We can modify the original condition and the question. If line A and line D are parallel, x+y=180. However, since conditions do not state that line A and line D are parallel to each other, the correct answer is E.
Attachments 1.png [ 8.45 KiB | Viewed 4635 times ]

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

In a certain school, teachers who lecture English and Spanish are there. If 2 teachers are selected randomly, what is the probability that at least one teacher selected lectures Spanish?
1) The ratio of Spanish teachers’ number to English teachers’ number is 3 to 1.
2) The sum of Spanish teachers’ number and English teachers’ number is less than 20.

If we modify the original condition and the question, there are two variables (E and S). In order to match the number of variables and the number of equations, we need 2 equations. Hence, there is high chance that the correct answer is C. Using the condition 1) and the condition 2), since (E,S)=(2,6),(3,9),(4,12), the answer is not unique and the conditions are not sufficient. Thus, the correct answer is E.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

n and k are positive integers. If n=(2^2)(3)(5^3)/15k, is n<k?
1) n<10
2) k>4

ANS: If we modify the original condition and the question, we get n=100/k, k=100/n. If we substitute this into n<k?, the question becomes n<100/n?, n2<100=102?, n<10?. Hence, the correct answer is A.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

Is x-intercept of y=ax+b greater than 0?
1) ab<0
2) a+b<0

ANS: If we modify the original condition and the question, the question becomes x-integercept=-b/a>0?, b/a<0?. If we multiply a^2, since it is a positive number, the sign of inequality does not change. Hence, it becomes ab>0?. So, since the condition 1) states ab<0, the answer is yes and the condition is sufficient. Hence, the correct answer is A.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If the average (arithmetic mean) of 9 numbers is 43, what is the standard deviation of them?
1) The smallest number of them is 43
2) The greatest number of them is 43

ANS: This is a recent trend question type. If range=M-m=0, mean=Max, or mean=min, then SD=0.
Condition 1) gives us mean=min, SD=0
Condition 2) also gives us mean=Max, SD=0. Hence, the correct answer is D.
- Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

Is x^2-y^2>x+y?
1) x<y
2) x+y<0

ANS: We can modify the original condition and the question. Then, the question becomes x^2-y^2>x+y? (x-y)(x+y)-(x+y)>0?, (x-y-1)(x+y)>0?. Then, since there are 2 variables, there is high chance that C is the correct answer. Using the condition 1) and the condition 2), the answer is always yes and the conditions are sufficient. Hence, the correct answer is C.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

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.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If m, n are positive integers, what is the value of mn?
1) m/n=7/15
2) The greatest common divisor of m and n is 3

ANS: There are 2 variables in the original condition. Hence, there is high chance that C is the correct answer. Using both the condition 1) and the condition 2), we get m=(7)(3) and n=(15)(3). Thus, the correct answer is C.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

In the x-y plane there is a line K, (x/a)+(y/b)=1. What is the x-intercept of line K?
1) a=2b
2) a=6

ANS: We can modify the original condition and the question. When the question asks about the x-intercept, we need to find the value of x when y=0. Then, if we substitute y=0, from x/a=1, we get x=a. Hence, we all need to know the value of a. Since the condition 2) states a=6, the condition is sufficient. Thus, the correct answer is B.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If P, Q, R are integers greater 1, have P and R common factors other than 1?
1) P and Q have common factors other than 1
2) Q and R have common factors other than 1

ANS: Since the original condition has 3 variables, we need 3 equations in order to match the number of equations and the number of variables. Thus, the correct answer is E.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If 2-digit positive integer n is 12 times of the tens digit of n, what is the value of n?
1) The tens digit of n is 3.
2) The sum of the tens digit and the units digit of n is 9.

There are 3 variables (n, a, b) and 1 equation (10a+b=12a) in the original condition. Since we need 1 more equation, the correct answer is D.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

Is (r^2)x>0?
1) r^5=1
2) x>0

ANS: There are two variables (r and x) in the original condition. In order to match the number of variables and the number of equations, we need 2 equations. Hence, the correct answer is C.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

A circle has the same area as a rectangle. What is the circumference of the circle?
1) The perimeter of the rectangle is 18
2) The area of the rectangle is 20

ANS: We can modify the original condition and the question. The area of the circle and the area of the rectangle are same. Hence, since it is asking for the circumference of the circle, we only have to know the area of the circle (which is same as the area of the rectangle). So, the correct answer is B.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

There are 3 integers, a, b, and c in that order. Are these integers consecutive?
1) a=c-2
2) b>a

We can modify the original condition and the question. In order for integers to be consecutive, they need to be a, b(=a+1), c(=a+2). Hence, the difference between c and a needs to be 2. Thus, the answer is yes for the condition 1). The correct answer is A.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

What is the median of prices?
1) More than 1/2 of the prices are \$1,500 or more than \$1,500
2) More than 1/2 of the prices are \$1,500 or less than \$1,500

ANS: There are many variables in this case. Hence, there is high chance that E is the correct answer. Using 1) and 2), we can see that “more than 1/2 of the prices are \$1,500 or more than \$1,500” and “more than 1/2 of the prices are \$1,500 or less than \$1,500”. The overlapping price then will be \$1,500. Thus, \$1,500 becomes the median, and the correct answer is C.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If Tom invest \$x April at a constant monthly interest rate of y percent, what is the percent increase from April to October?
1) x=10,000
2) y=2

ANS: If we modify the original condition and the question, we get x--> x(1+y%)^6. Hence, for the percent increase, we only have to know the value of y. Thus, the correct answer is B.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

Is y>0?
1) x^2<y^2
2) x+y=1

ANS: There are 2 variables in the original condition, Hence, since we need 2 equations, the correct answer is C.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

In the x-y plane, line K passes through (a,0) and (0,b). What is the slope of line K?
1) a/b=1
2) Line K passes through (1,2)

ANS: If we modify the original condition and the question, the slope of a line that passes through (a,0) and (0,b) is (0-b)/(a-0)=-b/a. Thus, the correct answer is A.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If ab≠0, √((5a+6b)/(a+3b))=?
1) b/a=2/3
2) a+b=5

ANS: If one of conditions is “number” and the other is “ratio”, the condition with “ratio” is the correct answer. Hence, the correct answer is A.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8029
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (DS)  [#permalink]

Show Tags

If ab≠0, is |a^b|=a^b?
1) |a|=a
2) |b|=b

ANS: If we modify the original condition and the question, the question becomes |a^b|=a^b? --> a^b≥0? --> a≥0?. Hence, the correct answer is A.
_________________ Re: Math Revolution Approach (DS)   [#permalink] 03 Jul 2016, 17:32

Go to page    1   2   3   4   5   6   7   8   9   10   11  ...  29    Next  [ 573 posts ]

Display posts from previous: Sort by

Math Revolution Approach (DS)

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

Moderator: souvonik2k

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne  