Question

Question 8
Which term of an AP : 21, 42, 63, 84, …. is 210?

A) $9^{th}$
B) ${10}^{th}$
C) ${11}^{th}$
D) ${12}^{th}$

Answer 1

Let nth term of the given AP be 210.
Here, first term,
a = 21
And common difference,
d = 42 – 21 = 21 and
$a_n$ = 210
$\because a_n=a+(n-1)d$
$\Rightarrow$ 210 = 21 + (n - 1)21
$\Rightarrow$ 210 = 21 + 21n - 21
$\Rightarrow$ 210 = 21n
$\Rightarrow$ n = 10
Hence, the 10th term of the AP is 210.