Summer is Coming! Join the Game of Timers Competition to Win Epic Prizes. Registration is Open. Game starts Mon July 1st.

 It is currently 16 Jul 2019, 09:44 ### 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 (PS)

Author Message
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If (4/9)÷n=3/5, n=?

A. 20/27
B. 27/20
C. 10/9
D. 9/10
E. 9/4

==>(4/9)÷n=3/5 -> (4/9)(1/n)=3/5. And 4/9n=3/5 -> n=(4/9)(5/3)=20/27.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

$$\frac{2^{x-1}}{2^{1-x}}$$ is equal to which of the following?

A. $$4^{x-1}$$
B. $$4^{1-x}$$
C. $$4^{2x}$$
D. $$4^{-2x}$$
E. $$4^x$$

==> You get $$\frac{2^{x-1}}{2^{1-x}} =2^{x-1-(1-x)}=2^{2(x-1)}=4^{x-1}$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

It’s well known that a company's profit=10,000x-50x^2, where x is the number of workers. If the profit of the company is the greatest, what is the value of x?

A. 5
B. 10
C. 50
D. 80
E. 100

==> From $$y=f(x)=ax^2+bx+c$$, if $$x=\frac{-b}{2a}$$, f(x) becomes either maximum or minimum. Thus, profit=$$-50x^2+10,000x$$, and in order for the profit to become the greatest, you get $$x=\frac{-10,000}{2(-50)}=100$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

What is the range of 25 consecutive even numbers?

A. 44
B. 46
C. 48
D. 50
E. 52

==> The number of consecutive even numbers=(The last number-the first number)/2 +1=range/2+1, so from range/2+1=25, range/2=25-1=24, you get range=2(24)=48.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If 1 male, 2 females, and 1 child are to be selected at random from 8 males, 10 females, and 8 children, respectively, how many such cases are possible?

A. 980
B. 1,440
C. 1,880
D. 2,480
E. 2,880

==> From (8C1)(10C2)(8C1)=(8)(10*9/2!)(8)=2,880, the answer is E.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

When $$5^{11}$$ and $$2^n7^2$$ have the same number of factors, what is the value of n?

A. 2
B. 3
C. 4
D. 5
E. 6

==> From 11+1=(n+1)(2+1), you get 12=3(n+1), and n-3.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If $$x^{-2}+x^{-1}=0$$, $$x=$$?

A. -1
B. 0
C. 1
D. 0, 1
E. -1, 0

==> If you multiply x^2 on both sides, you get 1+x=0, x=-1.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

Attachment: a.png [ 1.09 KiB | Viewed 606 times ]

If the distances between two consecutive points are the same, what is the value of A in terms of x and y?

A. 3y-2x
B. 3x-2y
C. 2x-3y
D. 2y-3x
E. 3y+2x

==> The distance between 2 consecutive points=d, hence d=y-x and A=y+2d=y+2(y-x)=3y-2x.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If 3 juniors from 8 juniors are selected at random to make a committee, how many cases are possible?

A. 8
B. 28
C. 35
D. 42
E. 56

==> In general, you solve probability questions using nCr, a combination. In other words, from 8C3=56, the answer is E.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If xy>0, which of the following must be positive?

A. $$x$$
B. $$y$$
C. $$x^2y$$
D. $$y^2x$$
E. $$x^3y$$

==> Squares are always positive, so the inequality sign doesn’t change even if you multiply or divide. Thus, from xy>0 and $$(x^2)xy>(x^2)0$$, you get $$x^3y>0$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If $$a>b>0$$, $$a^2+b^2=6ab$$, $$\frac{(a+b)}{(a-b)}=$$?

A. 1

B. $$\sqrt{2}$$

C. $$\sqrt{3}$$

D. $$\sqrt{5}$$

E. 2

==> From $$(a+b)^2=a^2+b^2+2ab=6ab+2ab=8ab$$, you get $$a+b=\sqrt{8ab}$$
And from $$(a-b)^2=a^2+b^2-2ab=6ab-2ab=4ab$$, you get $$a-b=\sqrt{4ab}$$ and
$$\frac{(a+b)}{(a-b)}=\sqrt{8ab}/\sqrt{4ab}=2$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

Attachment: a.png [ 3.61 KiB | Viewed 579 times ]

Attachment: b.png [ 2.23 KiB | Viewed 579 times ]

From the above, you get $$h:(s-r)/2=√3:1$$ and $$h=√3(s-r)/2$$. The answer is A.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

1-0.000001=?

A. 1.001*0.999
B. 1.0001*0.9999
C. 1.001*0.9999
D. 1.0001*0.999
E. 1.01*0.99

==> You get $$a^2-b^2=(a+b)(a-b)$$, and thus $$1-0.000001=1^2-0.001^2=(1+0.001)(1-0.001)=1.001*0.999$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

When a certain coin is flipped, the probability that the coin will land on head or tail is 1/2 each. If the coin is flipped 4 times, what is the probability that it will land on tail at least twice on 4 flips?

A. $$\frac{3}{8}$$
B. $$\frac{1}{16}$$
C. $$\frac{1}{2}$$
D. $$\frac{5}{8}$$
E. $$\frac{11}{16}$$

==> In general, you solve probability questions using nCr combination. In other words, from TTHH, there are (4!/2!/2!)=6 possibilities, so you get (1/2)(1/2)(1/2)(1/2)*6=3/8. From TTTH, there are (4!/3!)=4 possibilities, so you get (1/2)(1/2)(1/2)(1/2)*4=1/4. From TTTT, there is only 1 possibility, so you get (1/2)(1/2)(1/2)(1/2)=1/16 and (3/8)+(1/4)+(1/16)=(6+4+1)/16=11/16.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

Which of the following is equal to $$\frac{(n+2)!}{n!}$$?

A. $$n(n+1)$$
B. $$1+(\frac{2}{n})$$
C. $$n^2+3n+2$$
D. $$n^2+2n$$
E. $$n+2$$

==> Since (n+2)!=(n+2)(n+1)n!, from (n+2)!/n!=(n+2)(n+1)n!/n!=(n+2)(n+1)
=$$n^2+3n+2$$, the answer is C.
_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

When a/b=1.2, (a-b)/(a+b)=?

A. $$\frac{1}{15}$$
B. $$\frac{1}{11}$$
C. $$\frac{1}{9}$$
D. $$\frac{3}{8}$$
E. $$\frac{1}{3}$$

==> From a/b=1.2=6/5, if you substitute a=6 and b=5, you get (a-b)/(a+b)=(6-5)/(6+5)=1/11.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If two times x is 5 greater than three times y, what is the value of y, in terms of x?

A. y=2x-5
B. y=6x-5
C. y=(x/2)-5
D. y=(x/3)-5
E. y=(2x-5)/3

==> According to the ivy approach, is:”=”, greater than:”+”, hence you get 2x=5+3y. Thus, from 3y=5-2x, y=(2x-5)/3, the answer is E.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If the sum of the annual salary of n persons is $x and the monthly salary per person is$y, what is the value of n in terms of x and y?

A. $$\frac{x}{12y}$$
B. $$\frac{12x}{y}$$
C. $$12xy$$
D. $$\frac{12y}{x}$$
E. $$\frac{xy}{12}$$

==> If the annual salary per person: s, you get ns=x, s=12y. If you substitue this, you get n(12y)=x, $$n=\frac{x}{12y}$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

$$(5+\frac{1}{5})^2-(5-\frac{1}{5})^2$$=?

A. 2
B. 3
C. 4
D. 5
E. 9

==> Since $$a^2-b^2=(a-b)(a+b)$$, you get $$(5+\frac{1}{5})^2-(5-\frac{1}{5})^2=[(5+\frac{1}{5})-(5-\frac{1}{5})][(5+\frac{1}{5})+(5-\frac{1}{5})]=(\frac{2}{5})(10)=4$$.

_________________
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 7588
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Math Revolution Approach (PS)  [#permalink]

### Show Tags

If n is the product of 3 consecutive integers, which of the following must be true?

I. a multiple of 2 II. a multiple of 3 III. a multiple of 4

A. I only
B. II only
C. III only
D. I and II only
E. II and III only

==> From n=m(m+1)(m+2) , where m=integer, the product of 3 consecutive integers is always a multiple of 6. Thus, I and II is always true. For III, if m=1, from n=(1)(2)(3)=6, it is not a multiple of 4, hence it is false.

_________________ Re: Math Revolution Approach (PS)   [#permalink] 30 Apr 2017, 18:13

Go to page   Previous    1  ...  7   8   9   10   11   12   13  ...  29    Next  [ 568 posts ]

Display posts from previous: Sort by

# Math Revolution Approach (PS)

Moderator: souvonik2k   