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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?

If you liked this problem, here is an NRICH task that challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.