Positive integers from 1 to 9, inclusive, are written on 9 pieces of paper respectively and then put into 9 boxes. Someone randomly selects a number from the box for three times without replacement and uses these three numbers as the hundreds digit, tens digit and units digit of a three-digit integer.
Quantity A
The probability that the three-digit number is greater than 600
Quantity B
$$\frac{4}{9}$$