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UKMT Grey Kangaroo, 2015

Combinatorics Difficulty 3.0 AMC 10/12 Find the answer United Kingdom

In a mob of kangaroos, the two lightest kangaroos together weigh $25\%$ of the total weight of the mob. The three heaviest kangaroos together weigh $60\%$ of the total weight. How many kangaroos are in the mob?

(A) $6$ (B) $7$ (C) $8$ (D) $15$ (E) $20$

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