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 ca n'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 ?