You wake up one morning and there’s been a power outage. You know you have 12 black socks and 8 blue ones. How many socks do you need to pull out before you’ve got a match?

You will need to pull out 3 socks, not 9 socks.

As there are only 2 different colours, you will just need 3 socks to guarantee that 2 socks are of the same colour.