Question

Question 9
If the common difference of an AP is 5, then what is $a_{18}-a_{13}$.

A) 5
B) 20
C) 25
D) 30

Answer 1

Given, the common difference of the AP, i.e., d = 5
$a_{18}-a_{13}$
$=a+(18-1)d-[a+(13-1\left)d\right][\because a_n=a+(n-1\left)d\right]$
$=a+17\times 5-a-12\times 5$
$=85-60=25$