## Question

`In the series 3, 9, 15, … what will be the 21`^{st} term?

`In the series 3, 9, 15, … what will be the 21`^{st} term?

A. 121

B. 123

C. 111

D. 117

**Answer: B. 123**

**Solution:**

Clearly, 3 + 6 = 9, 9 + 6 = 15,….

So, the series is an A.P. in which a = 3 and d = 6.

∴ 21st term = a + (21 – 1) d

= a + 20d

= 3 + 20 × 6

**= 123.**