5
6
32C3 = 4960
45
Six combinations: 123, 132, 213, 231, 312, 321
Assuming you are treating each number as a number and not as an individual unit, the numbers you can make from these digits are 899, 989 and 998.
017, 071, 107, 170, 701, 710. 6 combinations
10
9*9*9 = 729 using the digits 1 to 9 and 2*9 using 10 and another digit. 749 in all.
We notice that you said "combinations of three digits". You didn't say "3-digit numbers".There are (10 x 10 x 10) = 1000 combinations of three digits.The only combinations of 3 digits that form numbers less than 15 are 000, 001, 002, . . .012, 013, and 014. There are 15 of those.So the remaining (1000 - 15) = 985 are all larger than 15.
-8
To calculate the number of license plate combinations using three letters and four numbers, we consider the possibilities for each part separately. There are 26 letters in the English alphabet, so for three letters, there are (26^3) combinations. For the four numbers, using digits 0-9, there are (10^4) combinations. Therefore, the total number of combinations is (26^3 \times 10^4), which equals 17,576,000 combinations.
There are 720 combinations if you use each of the digits only once per combination.