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'Weekly Problem 9 - 2014' printed from http://nrich.maths.org/
If Matt takes 12 jellybeans then he will have taken at least one of each flavour unless he takes all 8 watermelon jellybeans and either all 4 vanilla jellybeans or all 4 butter popcorn jellybeans. In this case the 4 remaining jellybeans will all be of the flavour he has yet to take, so taking one more jellybean ensures that he will have taken at least one of each flavour.
Therefore Matt should take 13 jellybeans.
This problem is taken from the UKMT Mathematical Challenges.View the previous week's solutionView the current weekly problem