Question: how many combinations are there in the range 000 999 where all three digits are different?
Answer: Assuming the digits 0 through 9 can be used, and a number can be repeated in the combination, then there are 10^3 possible combinations (1000 - from 000 to 999). If three different numbers have to be used, then 10 x 9 x 8 = 720 possible combinations.