In a group of kangaroos, the two lightest kangaroos weigh 25% of the total weight of the group. The three heaviest kangaroos weigh 60% of the total weight. How many kangaroos are in the group?
If 2 lightest Roos weigh 25%of the total, that means each weighs on average =25% / 2 =12.5%
If 3 heaviest Roos weigh 60% of the total, that means on average each weighs =60%/3 =20%
But the total weight of the 5 animals =25% + 60% =85%. So, 100% - 85% =15% is the total weight of the remaining animal(s). But 15% cannot be split among more than one animal, because they would be LIGHTER than the two light animals given.
Therefore, we must conclude that the remaining 15% belongs to one other Kangaroo. Or there must be 1 more Kangaroo for a total of 6.