Suppose you have 19 black socks and 19 green socks in the dryer. 4. without looking, how many socks would you need to pull out of the dryer to be sure you get a black pair?

You want to guarantee that you get a pair of black socks

if you had extrememly bad luck, you pulled out all the green socks, that's 19 socks, then you pulled out 2 which, of course, are both black

so it would be 19+2 or 21

you would need to pull out 21 socks to be absolutely sure you got at least 1 pair of black socks