In the arrangement of five dominoes shown in Figure 1, obeying the usual rule that adjacent squares have matching numbers, the two at the end total five spots, and so do the three in the middle. There are three other ways to achieve this, not counting left-right reflections as different. Can you find them?

### D18. Domino Design

*Contributed by Ian Stewart, University of Warwick*

*This problem originally appeared in the* Prisoner’s Dilemma *in the 2024 Spring issue of the PMP Newsletter. Solutions are no longer being accepted for this Dilemma.*