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'Collecting Marbles' printed from http://nrich.maths.org/
A bag contains hundreds of glass marbles, each one coloured either red, orange, green or blue. There are more than 2 marbles of each colour.
Marbles are drawn randomly from the bag, one at a time, and not replaced.
How many marbles must be drawn from the bag in order to ensure that at least three marbles of the same colour are drawn?
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This problem is taken from the UKMT Mathematical Challenges.