Question

Which term in the $\text{A.P.}5,13,21,...$ is $181$?

• A. ${21}^{\text{st}}$
• B. ${22}^{\text{nd}}$
• C. ${23}^{\text{rd}}$
• D. ${24}^{\text{th}}$

Answer 1

The correct option is C ${23}^{\text{rd}}$

Given sequence is $5,13,21,...$

Given: $a=5,d=8,n^{th}\text{term}=181$

To find: $n$
$\because t_n=a+(n-1)d⟹181=5+(n-1)8⟹181=5+8n-8⟹181=8n-3⟹8n=184⟹n=23$.

$\therefore$ $181$ is the ${23}^{\text{rd}}$ term.