Find the sum of all integers between 84 and 719, which are multiple of 5.
The required series is 85, 90, 95, ... , 715
Let there be n terms in the A.P.
We have, a = 85, d = 5
Then,
nth term = 715
715 = 85 + (n - 1)5
n = 127
Then,
Sn=n2[a+l]S127=1272[85+715]=50800