Question

Find the sum of 4+7+10+.... to 20 terms using the formula​

Answer 1

Answer:

Find the sum of 4+7+10+.... to 20 terms using the formula .

The above series is in A.P.

So,

a = 4 and d = 3

n = 20

__

Solution :

Sum of n-terms =

$\frac{n}{2} \times (2a + (n - 1)d) \\ \\ = 10(8 + 19 \times 3) \\ = 10 \times (8 + 57) \\ = 80 + 570 = 650$