Q.
In a geometric progression the ratio of the sum of the first 5 terms to the sum of their reciprocals is 49 and sum of the first and the third term is 35.The fifth term of the G.P. is
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a
7
b
7/2
c
7/4
d
7/8
answer is C.
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Detailed Solution
Let five terms in G.P. be ar2, ar, a, ar, ar2Then ar−2+r−1+1+r+r2(1/a)r2+r+1+r−1+r−2=49⇒ a2=49⇒a=±7.Also, ar2+a=35Therefore a = – 7 is not possibleThus, a=7 and a/r2=28.Now, fifth term =ar2=aa28=74
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