Question

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

Answer 1

Answer:

860

Step-by-step explanation:

a = 5, d = 4

Sn = n/2 (2a + (n-1)d)

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