Question

Which term of the AP: 2, 7, 12,... will be 77?

Answer 1

Here, first term $a=2$ and common difference $d=5$.
Let 77 be the nth term of given AP. Therefore,
$a_n=77$

$\Rightarrow a+(n-1)d=77$
$\Rightarrow 2+(n-1)5=77$
$\Rightarrow n-1=15\Rightarrow n=16$
Hence, 77 is the ${16}^{th}$ term of AP.