Sock Quiz

Courtesy of Mental Floss:

Half asleep and not looking, Jerry reached in
the clothes dryer to grab a pair of socks.
Inside the dryer are his 12 black socks,
his 7 blue socks, and his 2 green socks.

Now, Jerry doesn’t care WHAT color socks he wears;1
he just wants a pair that matches.

What’s the minimum number of socks Jerry would
have to blindly pull out of the dryer to ensure that
he has at least one pair of matching socks?

 Check out Mental Floss for the ANSWER.
Step 1

1. that should be obvious, since he owns green socks