If you only use each digit once the number is 6 (it is a simple permutation and 3!=6).
If you can repeat the digits there are 9 possible 3-digit numbers that start with 6, 9 that start with 7, and 9 that start with 8, giving you 27 possibilities.
There are 4 possible numbers if the digits are not repeated; 18 if they are. Those are 3-digit numbers, assuming that zero would not be a leading digit. If zero is allowed for a leading digit, then you can have 6 for the non repeated, and 27 if repetition.
48 of them if digits may not be repeated. 100 if they can.
You can make 4*4*4 = 64 numbers.
Assuming no repeated digits, lowest first, 20; in any order 120; Allowing repeated digits: 216
There are 60480 numbers.
Using the digits of 1345678, there are 210 three digit numbers in which no digit is repeated.
There are 4 possible numbers if the digits are not repeated; 18 if they are. Those are 3-digit numbers, assuming that zero would not be a leading digit. If zero is allowed for a leading digit, then you can have 6 for the non repeated, and 27 if repetition.
27 if the digits can be repeated. 6 if not.
48 of them if digits may not be repeated. 100 if they can.
24680 using only even numbers or 12346 which is an even number
You can make 4*4*4 = 64 numbers.
-- If the same digit may be repeated, then 64 can be made. -- If the same digit may not be repeated, then 24 can be made.
Since there are only five different digits, a 6-digit number can only be generated if a digit can be repeated. If digits can be repeated, the smallest 6-digit number is 111111.
If you're limited to only 5 digits that can't be repeated, then there are 120 ways they can be arranged.
151200 numbers.
There are twelve possible solutions using the rule you stated... 13,14,17,31,34,37,41,43,47,71,73 & 74
If they can be repeated, 343 different numbers. If they can be used once each, there are only 210.