80,63, 72,72,64,81,56,? | series Logical reasoning | WBCS

Complete the series by finding the missing number from the given options.

80,63, 72,72,64,81,56,?

(a) 96
(b) 98
(c) 89
(d) 90

Correct Answer: d

Solution:  

Method 1:

series 1:
80-8=72
72-8=64
64-8=56

series 2: 
63+9=72
72+9=81
81+9=90

Method 2:

Two series are there

Series 1: 80/8=10, 72/8=9, 64/8=8, 56/8=7
Series 2: 63/9=7, 72/9=8, 81/9=9, 90/9=10