It could be: 4760 = 1
0
1
Using a calculator will make it easier
The smallest four digit number is 1000. It is even so 1001 is the smallest four digit number that is odd.
It could be: 4760 = 1
3 x 4 x 4 x 4 = 192 of them
4067, 4076, 4607, 4670, 4706, 4760, 6047, 6074, 6407, 6470, 6704, 6740, 7046, 7064, 7406, 7460, 7604, 7640.
0
1234
Since the 1-digit number is explicitly required to be positive but the 2-digit number is not so constrained, the obvious solution is to make the 2-digit number negative. This gives 9*(-99) = -891
1
what is the largest 4-digit number you can make
In order to make the smallest possible number with a set of digits, you want the least valued number in the greatest valued place. For 5 digits, you would want the least digit, 0, in the ten thousands place. You would then want the second least digit, 3, in the thousands place, and so on. For the digits 0,3,5,7,9 the smallest possible number would therefore be 03,579 or 3,579.
1234, if you don't repeat any.
It is already a four-digit number.
100012