Question

(5 + 13 + 21 + ... + 181) = ?

विकल्प

• 2476

• 2337

• 2219

• 2139

Answer 1

2139

Explanation:

Let the number of terms be n.

Then, T_n = 181.

∴ 5 + (n – 1) × 8 = 181

⇒ (n – 1) × 8 = 176

⇒ (n – 1) = 22

⇒ n = 23

∴ Sum = `n/2 (a + l)`

= `23/2 (5 + 181)`

= `23/2 (186)`

= 23 × 93

= 2139