Marble Pairs
You’re given a jar containing 100 marbles, each one coloured either black or white, and there is at least 1 marble of each colour. You notice that if you pick any 2 marbles from the jar, at least one will be white. How many black marbles are there?
Solution
There is 1 black marble. If there are at least 2 black marbles, then it’ll be possible to pick a pair of black marbles, violating the property of always having at least 1 white marble.
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