Question

Find the sum of 20 terms of the A.P. 1, 4, 7, 10, ......

• A. 590
• B. 600
• C. 570
• D. 580

Answer 1

The correct option is A

590

Let a be the first term and d be the common difference of the given A.P. Then, we have a = 1 and d = 3.

We have to find the sum of 20 terms of the given A.P.

Putting a = 1, d = 3, n = 20 in

$S_n$ = ($\frac{n}{2}$) [2a + (n – 1) d],

We get

_{$S_{20}$} = ($\frac{20}{2}$) [2 $\times$ 1 + (20 – 1) $\times$ 3] = 10 $\times$ 59 = 590