I think this is a fantastic idea, with a patch that is much easier than those suggested by the other responses. Simply tell everyone that for the purposes of this exercise, only that information directly presented in the example is to be considered. People sometimes overlook relevant information or clever third options, and these situations are to be judged only based on the data being considered by the hypothetical person in the given scenario.

If there is any concern about this set up encouraging people to think about things with an insufficient amount of thoroughness, you can save some time at the end for a just-for-fun period where everyone gets to offer their clever workarounds and extra information that would have changed what the proper decision was, had it been considered.