Image via WikipediaIn your bedroom you have a drawer with 2 red, 4 yellow, 6 purple, 8 brown, 10 white, 12 green, 14 black, 16 blue, 18 grey, and 20 orange socks. The socks are all jumbled together in the drawer. It is dark in your bedroom, your partner is still asleep and so you don't want to turn on the light to see. So you cannot see which sock is which in the dark.
You are packing for a trip that will take you three days, so you need three pairs of socks.
How many socks do you need to take out to be sure that you have at least three pairs of socks of the same color?