4p3*3p1 equal to 72 ways
10000000000000000000000000000000000000000
24680
24
The answer is 3*3*2*1 = 18. If the leading digit is 0 it is not a 4-digit number.
502 205 250 520 4 numbers. If a leading zero is allowed then you can have 052 and 025 for 6 numbers.
10 x 9 x 8 = 720.
24680
There are 840 4-digit combinations without repeating any digit in the combinations.
24
18, if leading 0s are disallowed.
93,876
468, 486, 648, 684, 846, 864.
The answer is 3*3*2*1 = 18. If the leading digit is 0 it is not a 4-digit number.
502 205 250 520 4 numbers. If a leading zero is allowed then you can have 052 and 025 for 6 numbers.
10 x 9 x 8 = 720.
Six of them.
There are twelve possible solutions using the rule you stated.
60