Question

If the 7^th  term of an AP is 20 and its 11^th  term is 40 then, what will be the common difference?

(a) 3

(b) 4

(c) 5

(d) 2

The question was asked in an online quiz.

The query is from Nth Term of Arithmetic Progression topic in division Arithmetic Progressions of Mathematics – Class 10

Answer 1

The correct answer is (c) 5

Explanation: Here 7^th  term = 20

11^thterm = 40

Let the first term of the AP be a and common difference be d

T7 = a + (n – 1)d = 20

T7 = a + (7 – 1)d = 20

T7 = a + 6d = 20      (1)

T11 = a + (n – 1)d = 40

T11 = a + (11 – 1)d = 40

T11 = a + 10d = 40      (2)

Subtracting (1) from (2)

We get,

a + 10d – (a + 6d) = 40 – 20

4d = 20

d = 5