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Question

Find the number of terms in the series 20,1913,1823,__________ of which the sum is 300, explain the double answer.

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Solution

a=20,d=23 and let Sn=300.
(n/2)[2.20+(n1)(2/3)]=300.
Simplifying n261n+900=0
or (n25)(n36)=0
n=25 or 36.
Since common ratio is negative and S25=S36=300, it shows that the sum of last eleven terms i.e., T26,T27,....T36 is zero.

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