SUM OF AN AP 1

The first term of an AP is 8 and the last term is 57.If the arithmetic progression consists of 20 terms, calculate the sum of all the terms. 

Solution

A₁ = 8, n=20, A_n = 57

S_n = n(A₁ + A_n)

     2

S₂₀ = 20(8 + 57)

      2

S₂₀ = 10 x 65

S₂₀ = 650

Hence the sum of all 20 terms is 650.

TRY THIS.....................

The first term of an AP is 17 and the last term is 65. If the arithmetic progression consists of 40 terms, calculate the sum of all the terms.