Question

what is the sum of all postive integer lying between 200 and 400 that are multiple of 7

Answer 1

Least number divisible by 7 and above

200 is 203.

Greatest number divisible of 7 and below

400 is 399.

Total numbers divisible by 7 between

200 to 400 are 29

Now, sum of n terms of AP = n2n2 (a + 1)

where, a = 203, 1=399 and n = 29

= 292292(203+399)

= 8729