Question

The sum of A.P. 4, 7, 10, 13, ........ upto 20 terms is ______.

विकल्प

• 650

• 10 × 27

• 510

• 1300

Answer 1

The sum of A.P. 4, 7, 10, 13, ........ upto 20 terms is 650.

Explanation:

Let a be the first term and d be the common difference of given A.P.

Then a = 4; d = 7 – 4 = 3

We know that

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

∴ `S_20 = 20/2[2 xx 4 + (20 - 1)3]`

= 10[8 + 57]

= 650