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Which of the following numbers will replace the question mark (?) in the given series? 18, 71, 21, 76, 24, 81, 27, 86, 30, ?
Question

Which of the following numbers will replace the question mark (?) in the given series?
18, 71, 21, 76, 24, 81, 27, 86, 30, ?

A.

80

B.

82

C.

91

D.

83

Correct option is C

Given: 18, 71, 21, 76, 24, 81, 27, 86, 30, ?
Logic: 
Odd positions:  increasing by 3 each time.
Even positions: increasing by 5 each time.
Odd positions (starting with 18):
18 + 3 = 21
21 + 3 = 24
24 + 3 = 27
27 + 3 = 30
Even positions (starting with 71):
71 + 5 = 76
76 + 5 = 81
81 + 5 = 86
86 + 5 = 91
So, the missing number is 91.
Thus, correct option is (c).

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