Permutations or Combinations or Common Sense?
You have 12 black socks and 12 white socks mixed up in a drawer. You’re
up very early and it’s too dark to tell them apart. What’s the smallest
number of socks you need to take out (blindly) to be sure of having a
matching pair?
To know what it is click here!
Source
To know what it is click here!
Source