A certain state's lottery game, LOTTO, is set up so that each player pays $1 per ticket and chooses six different numbers between 1 and 20 inclusive. If the six numbers chosen match the six numbers drawn, the player wins the grand prize.

If a person buys one LOTTO ticket, what is his probability of winning the grand price?

Hint - this has to do with combinations - in this case the number of possible combinations of 6 items selected from 20. What does your text say about calculating combinations?