Question

If the sum of the first 2n terms of 2, 5, 8…. is equal to the sum of the first n terms of 57, 59, 61…., then n is equal to

• A. 10
• B. 12
• C. 11
• D. 13

Answer 1

Answer: (C)

11

Answer 2

We have, $\frac{2n}{2}\{ 2 \times 2 + (2n - 1)3\} = \frac{n}{2}\{ 2 \times 57 + (n - 1)2\}$

⇒ $6n + 1 = n + 56$

⇒ $n = 11$