You have 100 coins laying flat on a table, each with a head side and a tail side. 10 of them are heads up, 90 are tails up. You can't feel, see or in any other way find out which side is up. Split the coins into two piles such that there are the same number of heads facing up in each pile. How did you do it?
If two coins are tossed 5 times, what is the chance that there will be 5 heads and 5 tails?