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.