There are twelve possible solutions using the rule you stated... 13,14,17,31,34,37,41,43,47,71,73 & 74
500
It is 120 if the digits cannot be repeated.
4*3*2*1 = 24
If the digits may not be repeated, there are 6x5x4x3x2x1 = 720 numbers, If digits can be repeated, the answer is 6x6x6x6x6x6 = 46,656 numbers If zero is ong the available digits but is excluded from the first place. 5x6x6x6x6x6=38,880 numbers
That would be 4! = 4 * 3 * 2 * 1 = 24
24
500
There are 7,290 different 4-digit numbers that can be formed from the digits 1-9 without repetition.
There are 5*4*3 = 60 such numbers.
1 set
It is 120 if the digits cannot be repeated.
27 three digit numbers from the digits 3, 5, 7 including repetitions.
There are 5! = 120 such numbers.
3x3x3=27
4*3*2*1 = 24
48 of them if digits may not be repeated. 100 if they can.
36