If you're allowed to repeat the digits, then (5 x 5 x 5) = 125 can.
If you're not allowed to repeat the digits, then (5 x 4 x 3) = 60 can.
8
You can select 9 numbers for the first digit, 8 numbers for the second digit, and 7numbers for the third digit; so 504 (e.g. 9*8*7) different three digit numbers can be written using the digits 1 through 9.
102.
1,000
6, as long as they are all different
81 As there are no limits stated then you can have a number comprising a repeated single digit (such as 2222), two pairs of numbers (e.g. 2244) or three different numbers (such as 2462). The first digit can be one of any of the 3 numbers. The second digit can be one of any of the three numbers, as can the third digit and also the fourth. Then you can have 3 x 3 x 3 x 3 = 81 different 4-digit numbers using the three given numbers.
512
Forming three three digit numbers that use the numbers 1-9 without repeating, the highest product possible is 611,721,516. This is formed from the numbers 941, 852, and 763.
Any 3 out of 4 = 4. Each set can be arranged 6 ways so 24 different numbers.
5 x 10 x 5 = 250 different numbers, assuming there is no limit to each digits' use.
from 100 to 999 it is 900
27 three digit numbers from the digits 3, 5, 7 including repetitions.
8
You can select 9 numbers for the first digit, 8 numbers for the second digit, and 7numbers for the third digit; so 504 (e.g. 9*8*7) different three digit numbers can be written using the digits 1 through 9.
102.
1,000
6, as long as they are all different