Question

Find the sum of all the multiples of 5 which are three digit number??

Answer 1

AP:100,105,110..............995

a:100,d:5,an:995

an:a+(n-1)d

995:100+(n-1)5

885:(n-1)5

n:178

Sn:n/2[2a+(n-1)d

:89(200+885)

:89(1085)

Sn:96565