Find the wrong number in the series. 1, 2, 6, 15, 31, 56, 91

Question

Find the wrong number in the series.

1, 2, 6, 15, 31, 56, 91

A. 91

B. 31

C. 15

D. 56

Answer: A. 91

Solution:

The difference between the two consecutive numbers is 1, 4, 9, 16, 25, 35. (2-1, 6-2, 15-6, 31-15, …)

This is clearly , +(1²), +(2²), +(3²), +(4²), +(5²),+(6²)

Here 35 is wrong, So our wrong number is 91.

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