Question

Arithmetic mean of 2,5,8,... upto 13 terms = ______

• A. 10
• B. 12
• C. 16
• D. 20

Answer 1

The correct option is D 20

A.M of an arithmetic progression is given by,

A.M= $a_1+\frac{(n-1)d}{2}$
here $a_1$ is 2, n = 13 and d = 8-5 = 5-2 = 3

$\therefore$ A.M = $2+\frac{(13-1)3}{2}$

=$2+\frac{12\times 3}{2}$
= 20