EMNA Q.31

31Two new charity organizations C₁ and C₂ were formed, with x members each, on January 1, 2012. On first day of each, subsequent month, in C₁, number of members increases by a certain number a, while in C₂, number of members increases in such a way that ratio of the number of members in a month to the preceding month bear a ratio equal to b. On May 1, 2012, both organizations had the same number of members. If a = 20x, then b will be

Option : B
Explanation : Number of members in C₁ on May 1, 2012 = x + 4ya
Number of members in C₂ on May 1, 2012= xb⁴
x + 4a = xb⁴ and a = 20x
∴ x(b4 - 81)
As x ≠ 0, b4 - 81 = 0
∴ b = 3

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