MATHS
posted by BRENDON .
Could you please explain how to do this question? Thank you very much.
Gustav is an untidy man who keeps all his socks loose in his drawer. He has 6 pairs of white socks, 4 pairs of green socks and 5 pairs of black socks. What is the most number of socks Gustav will have to take out of his drawer to ensure he has a pair of socks of the same colour to wear?

He has 30 socks loose in the drawer. They are three different colors. If he takes four socks out of the drawer, at least two of them must be the same color.