Question

Find the sum of all multiples of 7 between 500 & 900

Answer 1

Hey!!! Liam here is yur answer :

Between any 2 numbers n1 and n2 (n2 > n1) there lie total of n2−n1+1 numbers and sum of all these numbers can be found out using the general formula

S=[(n1+n2)×(n2−n1+1)]/2

let, n1=501 and n2=899.

-> S1=700×399=279300

it can be seen that first number in the series which is multiple of 7 is 7*72 likewise the last number is 7*128.

Answer 2

33344 is the required sum