Question

the 1st term of an ap is 13 and the common difference is 5. find the sum of the first 20 terms​

Answer 1

Answer:

1080

Step-by-step explanation:

First term=13

C.D=5

Sum of first 20 terms:-

$\frac{20}{2} (13 + (20 - 1) \times 5) \\ = 10(13 + 95) \\ = 10(108) \\ = 1080$

Hope it helps you!

Answer 2

Question:-

The 1st term of an A.P. is 13 and the common difference is 5.

Find the sum of the first 20 terms

___________________________

Required Answer:-

Given:- First term = a = 13

Common difference = d = 5

To Find:-

Sum of first 20 terms = S20=?

Solution:-

tn = a + (n-1) x 5

t20 = (13) + (20-1) x (5)

t20 = 13 + 19 x 5

t20 = 13 + 95

t20 = 108

___________________________

Now to find the sum of first 20 terms,

Sn = n/2 x (t1 + tn)

S20 = 20/2 x (13 + 108)

S20 = 10 x (121)

S20 = 10 x 121

S20 = 1210

___________________________

Therefore Sum of first 20 term of an A.P. is 1210.

___________________________

Hope it help you.