Question

Which term of the AP: 21, 42, 63, 84,... is 210?

Options

• 9^th

• 10^th

• 11^th

• 12^th

Answer 1

10^th 

Explanation:

Let n^th term of the given AP be 210.

First term, a = 21

Common difference, d = 42 – 21 = 21 and a_n = 210

We know that the n^th term of an AP is

a_{n =} a + (n – 1)d

Where,

a = First term

a_n is n^th term

d is the common difference

210 = 21 + (n – 1)21

189 = (n – 1)21

n – 1 = 9

n = 10

So, 10th term of an AP is 210.