SEQUENCE AND SERIES A15

The first term of an AP is 5 and the last term is 57.If the arithmetic progression consists of 20 terms, calculate the sum of all the terms. 

Solution

A₁ = 5, n=20, A_n = 57

S_n = n(A₁ + A_n)

       2

S₂₀ = 20(5 + 57)

         2

S₂₀ = 10 x 62

S₂₀ = 620

Hence the sum of all 23 terms is 620.