A four digit positive number having all non-zero distinct digits is such that the product of all the digits is least. If the difference of hundreds digit and tens digit is 1, then total number of possibilities for that number are:
Since product is least so number will have digits 1, 2, 3, and 4
Difference is one so possibilities for hundreds and tens digit are 2,1 and 3,2 and 4,3
So possible number are 6
4 2 1 3
3 2 1 4
1 3 2 4
4 3 2 1
1 4 3 2
2 4 3 1