First, it all depends on how much money is in the pocket. You would add all of the money up and divide by how much there is then, change that into a fraction.. Then you would get your answer. For example lets say yo have a pocket with 5 pennies, 8 nickels, and 3 dimes. You add up the amount of coins, which is 16 coins. You pull out 4 coins, there is a 3/16 chance you would get 3 dimes.
Hope i helped.