Question

Find the sum of the first 100 positive integers exactly divisible by 7

Answer 1

Hi,

Explanation:

Number of multiple of 7:100

First+ last =7+700=707

sum= 100*707/2=35350

or

`\displaystyle 7+14+21+...+700=\sum_(i=1)^(100) 7*i\\=7*\sum_(i=1)^(100) i\\\\\\=7*(100*101)/(2)\\\\=35350\\`