Question

What is the sum of the first 20 terms of an A.P., if a  4 and t

20  36?​

Answer 1

Answer:

Given,

a= 4

20th term or last term for finding sum = 36

number of term = 20

Sum of n term =

(a + l) \times n \div 2(a+l)×n÷2

where

a= first term = 4

l = last term = 36

and n = no. of terms = 20

After substituting value

Sum = (4 + 36)X 20/2

= 40 X 10

= 400