SOLUTION: Find the sum of following series. 100, 93,86,79......................up to 20 terms

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Question 1048189: Find the sum of following series.
100, 93,86,79......................up to 20 terms



Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
n = 20; a1 = 93 d = -7
a20=a1*-7(n-1)=100+(19)(7)
=100+(19)(-7)=-33
Sn=n(a1+an)/2
=20(100-33)/2=-20(67)/2=10*67=670