Question

find the sum of integers between 10 and 500 which is divisible by 7

Answer 1

Solution

the integers between 10 and 500 which are divisible by 7 are ....

14,21,28,.........,497

now...

first term (a)=14

common difference (d)=7

last term(l)=497

now...let the term 497 is the nth term...

497=14+(n-1)7

=>497-14+7=7n

=>n=490/7=70

therefore the sum of 70 terem is

$s(70) = \frac{70(14 + 497)}{2} = 17885$

Hope this helps you