The largest number with no repeated digits is 9,876,543,210 although it is 10 digits long, the largest 3 digit number with no repeated digits is 987
It is 99,887,765
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
There are only two smaller 3-digit numbers and both of them have repeated digits.
Repeated twice means we're allowed three of them. That would be 88,866,644. If you really meant repeated, that would be 88,664,420
102 is the smallest three digit number with different digits.
Using the digits of 1345678, there are 210 three digit numbers in which no digit is repeated.
For this type of problems, you basically assign digits from left to right, choosing the largest digit, in every case, that satisfies the requirements.
27 three digit numbers from the digits 3, 5, 7 including repetitions.