103 and 301 .
"130" and "310" .
18 of them.
9630
If they can be repeated, 343 different numbers. If they can be used once each, there are only 210.
24 different numbers.
Assuming each of the given digits can be used only once, the answer is 24. If not, the answer is infinity.
"130" and "310" .
18 of them.
There are 7,290 different 4-digit numbers that can be formed from the digits 1-9 without repetition.
9630
If they can be repeated, 343 different numbers. If they can be used once each, there are only 210.
24 different numbers.
256
There are 5 numbers of 1 digit, 25 numbers of 2 digits, and 75 numbers of 3 digits. This makes 105 numbers in all.
The difference is 360.
120 There are 6 digits in total. The numbers with 3 digits, with all digits distinct from each other, are the permutations of the 6 digits taken 3 at a time, and therefore there are 6*5*4 = 120 of them.
3