The general rule is to imagine that you have four places in the number eg 9999 then calculate by saying 4 x 3 x 2 x 1 = 24. That gives you:
24 altogether if you allow numbers starting with ZERO. 18 otherwise.
SIX starting with 0:
0349
0394
0439
0493
0934
0943
SIX starting with 3:
3049
3094
3409
3490
3904
3940
SIX starting with 4:
4039
4093
4309
4390
4903
4930
SIX starting with 9:
9034
9043
9304
9340
9403
9430
-58264
Forming three three digit numbers that use the numbers 1-9 without repeating, the highest product possible is 611,721,516. This is formed from the numbers 941, 852, and 763.
9876543210
9,876,543,210 9876543210
There are 25 such numbers.
24
256
18, if leading 0s are disallowed.
Without repeating digits (not digets!) and without leading 0s, 600 of them.
98765
60
468, 486, 648, 684, 846, 864.
86420
It is a repeating decimal.
-58264
4 x 3 x 2 ie 24
5040