how many socks would you need to remove from a drawer containing 10 blue socks, 15 black socks and 5 red socks, to in sure that you have at least 2 matching socks?

Answer 1

You hardest time matching is if you picked one of each before you picked the second.
So, pick one blue, one black, one red, then pick one more. You have to get a matched pair in four picks.

Answer 2

Drawer containing 8 red socks 10 while socks and 4 blue socks