Question

Find the sum of 50 terms of the A.P. 1 + 4 + 7 + ..... .

Answer 1

a = 1

d = 4 − 1

= 3

n = 50

Using `S_n = n/2 [2a + (n - 1)d]`

`S_50 = 50/2 [2(1) + (50 - 1)3]`

= 25[2 + 49 × 3]

= 25[2 + 147]

= 25 × 149

= 3725