Class 10

Math

All topics

Arithmetic Progressions

The first term of an $A.P.$ is $5$, the common difference is $3$ and the last term is $80$, find the number of terms.

Given : $a_{1}=5,d=3$$,a_{n}=80$

$∴a_{n}=a_{1}+(n−1)d$

$80=5+(n−1)×3$

$75=(n−1)×3$

$n−1=375 $

$n−1=25+1$

$n=26$

Hence, This is answer.