Question

Which term of the A.P : $3,8,13,18,....,$is $78$.

Answer 1

According to question'

$a$, first term=$3$

$d$, comman difference=$5$

$78=a+(n-1)d$

$3+(n-1)5=78$

$\Rightarrow$ $n-1=\frac{78-3}{5}$

$\Rightarrow$ $n=15+1$

$\Rightarrow$ ${16}^{th}$ term