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.
How many possibilities are there of such number?
The product would be least if and only if 2 is at hundred's position and 1 is at 10's position.
that way two number are fixed for 100's and 10's position
now rest can be selected in 7c1x6c1=42 ways is your answer
Given the number 123456789. Find a permutation of the number's digits such, that the left most digit is evenly divisible by 1, the two left most digits are evenly divisible by 2, the three left most digits are divisibly by 3 and so on?