PK 2015 Q3
3. Mr Hyde can't remember exactly where he has hidden his treasure. He knows it is at least 5 m from his hedge, and at most 5 m from his tree. Which of the following shaded areas could represent the largest region where his treasure could lie?
Pink Kangaroo 2015, Question 3. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: A
Points which are at most 5 m from the tree lie on or inside a circle of radius 5 m with its centre at the tree. However, not all of the inside of the circle will be shaded because the treasure is at least 5 m from the hedge, so we should have an unshaded rectangular strip next to the hedge. This leaves the shaded region in A.
Solution © UK Mathematics Trust, from the PK 2015 solutions.