ARITH. PROGR. 1

The first term of an AP is 13 and the last term is 157.If the arithmetic progression consists of 20 terms, calculate the sum of all the terms. 

Solution

A₁ = 13, n=20, A_n = 157

S_n = n(A₁ + A_n)

       2

S₂₀ = 20(13 + 157)

         2

S₂₀ = 10 x 170

S₂₀ = 1700

Hence the sum of all 20 terms is 1700.

TRY THIS………….

The first term of an AP is 11 and the last term is 107.If the arithmetic progression consists of 30 terms, calculate the sum of all the terms.