Question

Find the sum of all the odd numbers from 1 to 101.

Answer 1

n = (an - a/d) + 1 = (101 - 1/2) +1 = (100/2 ) +1 = 50+1 =51
Sn = n/2 (a + an) = (1 + 101) 51/2 = 102 × 51/2 = 51 × 51 = 2601