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

Question

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

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