Question

What will come in place of question mark in the following number series ?

1, 3, 7, 15, ?, 63, 127

A 22
B 25
C 29
D 31
Answer & Explanation
Option: [D]

The pattern is

21 - 1 = 1

22 - 1 = 3

23 - 1 = 7

24 - 1 = 15

25 - 1 = 31

26 - 1 = 63

27 - 1 = 127

So, 31 will replace the question mark.

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