Question

Find ${}^{\prime }{n}^{\prime }$ if the $nth$ term of the following $A.P.$ is $70$ :
$7,10,13,16,.......$

Answer 1

Given:$a=7,d=3,t_n=70$

To find:number of terms$n$

$n^{th}$ term of an A.P$=a+(n-1)d$

$\Rightarrow 70=7+(n-1)3$

$\Rightarrow 70-7=(n-1)3$

$\Rightarrow n-1=\frac{63}{3}=21$

$\Rightarrow n=21+1=22$ terms.