Question

What is missing sequence number?
5 6 9 - 25 40

Answer 1

15

Explanation:

term 1 is equal to 5.

term 2 is equal to 5 + (1) = 5 + 1 = 6

term 3 is equal to 6 + (1 + 2) = 6 + 3 = 9

term 4 is equal to 9 + (1 + 2 + 3) = 9 + 6 = 15

term 5 is equal to 15 + (1 + 2 + 3 + 4) = 15 + 10 = 25

term 6 is equal to 25 + (1 + 2 + 3 + 4 + 5) = 25 + 15 = 40