34. If the nth term of an AP is 7-3n, find thesum of twenty five terms – InterviewSolution

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34. If the nth term of an AP is 7-3n, find thesum of twenty five terms. (CBSE 2012]

Answer»

First Term, a=7-3*(1)=4Second term=7-3*(2)=1d=1-4=-3

Sum of first 25 terms=( 25/2)*((2*4)+(25-1)*(-3))=(25/2)*(8-72)=-25*32= -800

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