ARITHMETIC PROGRESSION 1

The first term of an AP is 7 and the last term is 57.If the arithmetic progression consists of 20 terms, calculate the sum of all the terms. 

Solution

A₁ = 7, n=20, A_n = 57

S_n = n(A₁ + A_n)

       2

S₂₀ = 20(7 + 57)

         2

S₂₀ = 10 x 64

S₂₀ = 640

Hence the sum of all 23 terms is 640.

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The first term of an AP is 5 and the last term is 51.If the arithmetic progression consists of 30 terms, calculate the sum of all the terms.