Question

Find the sum of all multiples of 7 between 300 and 700

Answer 1

Here a series will be formed as 301, 308, 315, ...........700
So we have the first term a = 301 and d = 7 and last term l = 700
700 = 301+(n-1)7
399 = 7n-7
406=7n
n = 58

Sum = n/2(a+l)
Sum = 58/2(301+700)
= 29 x 1001
= 29029