GK 2016 Q17
17. Theo's watch is 10 minutes slow, but he believes it is 5 minutes fast. Leo's watch is 5 minutes fast, but he believes it is 10 minutes slow. At the same moment, each of them looks at his own watch. Theo thinks it is 12:00. What time does Leo think it is?
- A 11:30
- B 11:45
- C 12:00
- D 12:30
- E 12:45
Grey Kangaroo 2016, Question 17. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: D 12:30
Since Theo thinks it is 12:00, his watch shows 12:05. Therefore, the correct time is 12:15 since Theo's watch is 10 minutes slow. Since Leo's watch is five minutes fast, at 12:15 his watch will show 12:20. However, Leo thinks his watch is 10 minutes slow so he thinks the time is 12:30.
Solution © UK Mathematics Trust, from the GK 2016 solutions.