Question

Find the value of 7 + 15 + 23 +...+ 767 + 775 + 783

Answer 1

38,710.

Explanation:

This is an arithmetic series with common difference 8 , first term a = 7 and last term L = 783.

The number of terms n = (783 - 7) / 8 + 1 = 98

Sum of 98 terms = (n/2)[a + L)

= (98/2)(7 + 783)

= 49 * 790

= 38,710.