SUM OF AP - 1

The first term of an AP is 15 and the last term is 57.If the arithmetic progression consists of 20 terms, calculate the sum of all the terms. 

Solution

A₁ = 15, n=20, A_n = 57

S_n = n(A₁ + A_n)

      2

S₂₀ = 20(15 + 57)

        2

S₂₀ = 10 x 72

S₂₀ = 720

Hence the sum of all 23 terms is 720.

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The first term of an AP is 23 and the last term is 87.If the arithmetic progression consists of 30 terms, calculate the sum of all the terms.