1.   Choose the correct alternative that will continue the same pattern and replace the question mark in the given series.
5, 6, 9, 15, ?, 40



A. 21
B. 25
C. 27
D. 33

Answer: Option B

Explanation:

The pattern is + 1, +3, +6, .... i.e. +1, +(1, + 2), + (1+ 2 + 3), ........ So, missing term = 15 +(1+ 2 + 3 + 4) = 25.