In the series 3, 9, 15, ...... what will be the 21st term?

A. 117

B. 121

C. 123

D. 129

Answer: Option C

Solution(By Examveda Team)

Clearly, 3 + 6 = 9, 9 + 6 = 15,.....
So, the series is an A.P. in which a = 3 and d = 6.
Therefore 21st term = a + (21 - 1) d = a + 20d = 3 + 20 x 6 = 123.