In craps you can buy a number by giving the house a commission. The commission is normally five percent. Then when the number hits you will be paid at the true odds for that specific number. Buying the 4 and 10 is very common in craps and is cheaper. You tell the dealer you want to buy the 4, you then give the dealer $21 instead of $10. If the 4 comes before the 7, the house will payout you the true odds of 2 to 1, or $40 for $20. The 4 and 10 normal house odds payout will leave the house with a 6.7 percent profit. So the five percent commission is your advantage. The other numbers, 5,6,8 and 9, are cheaper to place bet then to buy. This will most certainly help your win-rate at the casinos craps table.