Multiple choice

A boy has 10 pairs of white socks and 10 pairs of black socks. He can pick only one piece each time. How many pieces of socks does he have to pick before he necessarily gets at least one matching pair?

  1. 3

  2. 11

  3. 21

  4. 22

  5. 31
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A Correct answer
Explanation

In the worst case scenario, the first two socks that the boy picks can be of different colours, i.e. one white and  one black.  Now, the 3rd sock that he picks will be either white or black that will pair with one of the 1st two socks. Hence upon drawing 3 socks, he will get a pair.

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