A town decides to run a local lottery based on the same model as the national lottery. There are only 20 numbers from which to pick, 1 to 20, and only four numbers are picked. Four winning numbers are selected from a drum-full of numbered balls plus a bonus ball. The top prize is for four correct numbers, the second prize is for three correct numbers plus the bonus ball and the third prize is for three correct numbers. What are the probabilities of winning each of these prizes with a single entry in the lottery?