GK 2015 Q20
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
Grey Kangaroo 2015, Question 20. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: A 6
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.
Solution © UK Mathematics Trust, from the GK 2015 solutions.