Which of the following numbers will replace the question mark (?) in the given series?
7, 13, 21, 31, ?

Correct option is D

The given series is: 7, 13, 21, 31, ?

The differences between consecutive terms.

13−7=6

21−13=8

31−21=10

The differences are increasing by 6,8,10,…

The next difference after 10 is 12.

31+12=43

Correct answer: (d) 43.