given an AP is required of all integers between 50 and 500, which are multiples of 7

To find: the sum of all integers between 50 and 500 which are divisible by 7

So, the sequence is 56, 63, 70….497

It is an AP whose first term is 56 and d is 7

Hence the sum is given by the formula

Now for the finding number of terms, the formula is

n = 64

Substituting n is the sum formula we get

s = 17696