Question

Find the sum of first 20 terms of of an ap whose first term is 5 common difference is 4

Answer 1

Step-by-step explanation:

a = 5

d = 4

n = 20

$sn \: = \frac{n}{2} (2a + (n - 1)d) \\ \\ s20 = \frac{20}{2} (2 \times 5 + (20 - 1) \times 4) \\ \\ = 10(10 + 19 \times 4) \\ \\ = 10(10 + 76) \\ \\ = 10 \times 86 \\ \\ = 860$

Hope it helps.