Question

If in an A.P., first term is 20, common difference is 2 and n^th term is 42, then find n.

(a) 10

(b) 11

(c) 12

(d) 14

The question was posed to me in homework.

I would like to ask this question from Arithmetic Progression(A.P.) topic in chapter Sequences and Series of Mathematics – Class 11

Answer 1

Right answer is (c) 12

Easiest explanation: We know, a=20, d=2, an=42.

a+(n-1) d = 42 => 20 + 2(n-1) = 42

=>2(n-1) = 42-20=22 => n-1 =11 => n=12.