Question

A.P 15, 10, 5, find sn of first 10term​

Answer 1

a= 15

d=5

n=10

Sn=n÷2(a+an)

an=a+(n-1)×d

=15+(9)×5

=15+45

=50

Sn=10÷2(15+50)

=5(65)

=325

so the sum of first 10 term is 325

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