Question

Find the sum of 1st 25th term of the Ap 7,11,15,9.......by using formula

Answer 1

★ Given :

A.P : 7, 11, 15, 19 ........

First term (a) = 7

Common Difference (d) = 4

Number of terms (n) = 25

$\rule{200}{1}$

★ To Find :

We have to find the sum of 1st 25th term of the A.P.

$\rule{200}{1}$

★ Solution :

We know that,

Sn = n/2 [2a + (n - 1)d]

→ Sn = 25/2 [2(7) + (25 - 1)4)]

→ Sn = 25/2 [14 + 24(4)]

→ Sn = 25/2 [14 + 96]

→ Sn = 25/2 * 110

→ Sn = 25 * 55

→ Sn = 1375