# Which term of an AP: 21, 42, 63, 84, … is 210?

Given: AP: 21, 42, 63, 84, … is 210

To find: n for which an = 210.

Formula Used: nth term of an AP is:

an = a + (n - 1) d

Explanation:

Let nth term of the given AP be 210.

Here, first term, a = 21

and common difference,

d = 42 – 21 = 21 and an = 210

As we know, nth term of an AP is

an = a + (n - 1) d

where a = first term

an is nth term

d is the common difference

210 = 21 + (n - 1 )21

189 = (n - 1 )21

n - 1 = 9

n = 10

So, the 10th term of an AP is 210.

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