20. 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
20. A The remaining kangaroos weigh $(100-25-60) \%=15 \%$ of the total weight. However, this cannot be made up of the weights of more than one kangaroo since the information in the question tells us that the lightest two weigh $25 \%$ of the total. Hence there are $2+1+3=6$ kangaroos in the mob.