Question

If twice the 11^th term of an AP is equal to 7 times of its 21^st term, then its 25^th term is equal to

(A)  24 

(B)  120 

(C)  0 

(D)  None of these

Answer 1

Correct option (C) 0

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

11^th term of AP = a + 10d

21^st term of AP = a + 20d

2(a + 10d) = 7(a + 20d)

⇒ 2a + 20d = 7a + 140d

5a + 120d = 0

⇒ a + 24d = 0 

Hence, the 25th term is 0.