Bunuel wrote:

If x is a positive integer and \(4^x – 3 = y\), which of the following CANNOT be a value of y ?

A. 1

B. 7

C. 13

D. 61

E. 253

NEW question from GMAT® Official Guide 2019

(PS04797)

Note:

x = positive integer

Given,

\(4^x\)-3=y

we are asked to find out which can't be the value of y. No specific value of x is given.

Trail and error is the way to get the correct answer. Assume the value of x = 1 , 2 , 3 , 4. All the option matches except B.

\(4^1\)-3=1

\(4^2\)-3=13

\(4^3\)-3=61

\(4^4\)-3=253

Thus , B is the correct answer.