Question

What is the $7^{th}$ term in an infinite H.P. $3+12+21+....?$

• A. $\frac{1}{17}$
• B. $\frac{1}{27}$
• C. $\frac{1}{47}$
• D. $\frac{1}{57}$

Answer 1

The correct option is D $\frac{1}{57}$

Given series is $3+12+21+....$

Here $a=3,d=9$
We know $a_n=\frac{1}{a+(n-1)d}$
$\Rightarrow a_7=\frac{1}{3+(7-1)9}$
$\Rightarrow a_7=\frac{1}{57}$