Question

The sum of all multiples of 5 lying between 101 and 999

Answer 1

the first multiple of 5 between 101 and 999is105 & last no.is995 so by putting

Answer 2

first number 105
last number 995
common difference 5
term number =n
995=105+(n-1)×5
890/5=n-1. n=179
sum=179/2×(105+995)
=(179×1100)/2
=179×550=98450