Question

The sum of how many terms in the series 7, 14, 21, 28......makes a sum of 952?

Answer 1

by using formula
Sn=n/2[2a+(n-1)d]

where
Sn=952
a=7
d=7
we have to find n =?
952=n/2 [2×7+(n-1)×7]
952×2=n [14+7n-7]
1904=n[7n+7]
1904=7n^2+7n
7n^2+7n-1904=0
7n^2+119n-112n-1904=0
7n (n+17)-112 (n+17)=0
(7n-112)(n+17)=0
n=112/7
n=16
n is not equal to (-17)

therefore n =16

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