ARITHMETIC PROGRESSION 4

The first term of an AP is 31 and the last term is 97.If the arithmetic progression consists of 20 terms, calculate the sum of all the terms. 

Solution

A₁ = 31, n=20, A_n = 97

S_n = n(A₁ + A_n)

       2

S₂₀ = 20(31 + 97)

         2

S₂₀ = 10 x 128

S₂₀ = 1280

Hence the sum of all 20 terms is 1280.

TRYTHIS………………….

The first term of an AP is 11 and the last term is 33.If the arithmetic progression consists of 40 terms, calculate the sum of all the terms.