Question

How many terms are there in the AP 7, 11, 15, ..., 139?

(a) 31
(b) 32
(c) 33
(d) 34

Answer 1

(d) 34

In the given AP, we have:
a = 7 and d = (11 - 7) = 4
Suppose there are n terms in the given AP. Then,
T_n = 139 ⇒ a + (n - 1)d = 139
⇒ 7 + (n - 1) × 4 = 139
⇒ 4n = 136
⇒ n = 34
Hence, there are 34 terms in the given AP.