JEE Main 2014 · 11 Apr · Shift 1 · Mathematics Q68

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MathematicsSingle correct+4 / -1Question 68 of 90

In a geometric progression, if the ratio of the sum of first 5 terms to the sum of their reciprocals is 49, and the sum of the first and the third term is 35. Then the first term of this geometric progression is :

Answer and worked solution

Official answer: C

The ratio of $S_5$ to the sum of the reciprocals is $a^2r^4$ . So $a^2r^4=49$ and $ar^2=7$ (the third term).

Then $a+ar^2=35$ gives $a=28$ .

Topics:Geometric progression

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JEE Main 2014 · 11 Apr · Shift 1, Mathematics question 68