Find the sum of the first 149 terms of an AP whose first term and third term are 180 and 190, respectively.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 81950.
a₃ = a + 2d = 190
⇒ 180 + 2d = 190
⇒ d = 5
Sn = (n/2) × [2a + (n - 1)d]
⇒ S149 = (149/2) × [2 × 180 + (149 - 1) × 5]
= 74.5 × [360 + 740]
= 74.5 × 1100
= 81950