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Obviously, the first one would take the least throws. But it could vary accordingly. If we get all ones for the first challenge, and get all sixes and fives for the other two, the second and third would take less throws. A trick for the last challenge is to wait until we get a 5. If not, we will have to wait until we get a 1 or a 2 where we will need to use up more throws. If we have only one plug left, it is very difficult to get a one for the dice. Here is a proof that it is possible for the first challenge to take more tries than the second and third.