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 $3,4,2,1,5$
SolUTION
$\mathbf{E}$

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 $\mathrm{E}$ 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.