20
you can make 6
6
6c4=15
720
type in your calculator C(6,4) like the combination of 6 things taken 4 at a time
20
you can make 6
6 ways
The answer is 6^6, or 46656.
You can make 5 combinations of 1 number, 10 combinations of 2 numbers, 10 combinations of 3 numbers, 5 combinations of 4 numbers, and 1 combinations of 5 number. 31 in all.
18
6
6c4=15
6 for 3-digits, 6 for 2-digits, 3 for 1-digits, and 15 for all of the combinations
720
the options i can see are: 1111111111 111111112 11111122 1111222 112222 22222 there are 6 combinations but i will need to reformulate to work out how many permutations of these 6 combinations there are