x = 2y; y is a positive integer. Quantity A: 4, Quantity B: 1/2^{-x}

Question

x = 2y; y  is a positive integer.

Quantity A  
4

Quantity B  
 \frac{1}{2^{-x}}

sanjitscorps18 · Answer

Sajjad1994 
The question is not clear. Nor are any options listed.
Please re-write this question.

Sajjad1994 · Answer

Hi

There is no issue with the question, as being a GRE Quantitative comparison, this question has always same answer choices.

A) Quantity A is greater. 
 B) Quantity B is greater. 
 C) The two quantities are equal. 
 D) The relationship cannot be determined from the information given.

So test takers usually memorize them.

mkeshri185 · Answer

Solution is not clear. how can we compare 4 with 1/2^-x? we just have given rel between x and y and on simplyfying B weger 2^x now 4 and 2^x how can we compare? If y>0 so if y=1 then x=2*1 = 2 then B = 2^2 so A=B but if y=2 then x=2*2=4 then 2^4>4. Which means relation is not clear. Answer should be D

Quantity A can be written as
[ltr](2^2)y=2^2y = 4.[/ltr]

you have written this so you are assuming y = 1?

Quantity A can be written as  
  (2^2)y=2^2y = 4.

you have written this so you are assuming y = 1?

Sajjad1994 · Answer

Explanation

Quantity 1:  4

Quantity 2:   \frac{1}{2^{-x}}=2x.

Since  x=2y:

2^x=2^{2y}=4^y.

So Quantity 2 is  4^y.

Comparison:

Quantity 1:  4
 Quantity 2:   4^y  with y a positive integer.

If  y=1,  Quantity  2 = 4^1=4  ----> equal.

If  y>1,  Quantity  2 >4.

Since  y  is a positive integer,  y≥1.

Answer: D

x = 2y; y is a positive integer. Quantity A: 4, Quantity B: 1/2^{-x}

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