November 2021 - Math Problem

A bag contains 10 blue blocks, 10 green blocks and 10 red blocks.  What is the minimum number of blocks you have to remove from the bag to ensure that you get 4 blocks of the same colour?

Solution:

You would have to remove 10 blocks to ensure that you get 4 blocks of the same colour.  

What if each bag started with 20 blocks of each colour?

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