Question

The sum of first 20 terms of the AP 10, 12, 14, 16, 18…. is _________

(a) 200

(b) 580

(c) 620

(d) 440

This question was addressed to me in an interview for internship.

The question is from Sum of N Terms of Arithmetic Progression topic in section Arithmetic Progressions of Mathematics – Class 10

Answer 1

Right option is (b) 580

For explanation I would say: Here a = 10, d = 2 and n = 20.

We know that, Sn = \(\frac {n}{2}\) (2a + (n – 1)d)

S20 = \(\frac {20}{2}\) (2(10) + (20 – 1)2)

S20 = 10(20 + 38) = 580