GK 2019 Q12
12. Jane was playing basketball. After a series of 20 shots, Jane had a success rate of 55%. Five shots later, her success rate had increased to 56%. On how many of the last five shots did Jane score?
- A 1
- B 2
- C 3
- D 4
- E 5
Grey Kangaroo 2019, Question 12. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: C 3
Since Jane had a success rate of 55% after her first 20 shots, the number of times she had scored out of 20 was 0.55 × 20 = 11. Similarly, since her success rate had increased to 56% after 5 more shots, the number of times she had scored out of 25 was 0.56 × 25 = 14. Hence the number of shots she scored out of the last five was 14 − 11 = 3.
Solution © UK Mathematics Trust, from the GK 2019 solutions.