20
The answer is 10C4 = 10*9*8*7/(4*3*2*1) = 210 ways.
32C3 = 4960
24
3 x 3 x 3 x 3 = 81 combinations
20
The answer is 10C4 = 10*9*8*7/(4*3*2*1) = 210 ways.
120 combinations using each digit once per combination. There are 625 combinations if you can repeat the digits.
32C3 = 4960
24
3 x 3 x 3 x 3 = 81 combinations
It is: 9C7 = 36
66
10,000
15
two: 36 and 63
9