GK 2020 Q15
15. Aisha has a strip of paper with the numbers 1, 2, 3, 4 and 5 written in five cells as shown. She folds the strip so that the cells overlap, forming 5 layers. Which of the following configurations, from top layer to bottom layer, is it not possible to obtain?
- A 3, 5, 4, 2, 1
- B 3, 4, 5, 1, 2
- C 3, 2, 1, 4, 5
- D 3, 1, 2, 4, 5
- E 3, 4, 2, 1, 5
| 1 | 2 | 3 | 4 | 5 |
Grey Kangaroo 2020, Question 15. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: E 3, 4, 2, 1, 5
The four figures (A) to (D) give a side-view of how the strip could be folded to give the arrangements of numbers in options A to D. Figure (E) shows that it is not possible to get option E since number 5 would end up between number 4 and number 2 (as indicated by the dashed line labelled 5) rather than below number 1 as is required.
Solution © UK Mathematics Trust, from the GK 2020 solutions.