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

Foundation

Mathematics Foundation

Sum of n terms of an AP

Question

2476

2219

2139

2337

College PredictorLive

Know your College Admission Chances Based on your Rank/Percentile, Category and Home State.

Get your JEE Main Personalised Report with Top Predicted Colleges in JoSA

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.

$∴ sum = \frac{n}{2} (a + ℓ) = \frac{23}{2} (5 + 181) = 23 \times 93 = 2139 .$