Question

Use numbers 2,3,4,5,7, and 8 exactly once to form two three-digit numbers P and Q. if P-Q is a positive number; the smallest possible value of P-Q is ......​

Answer 1

The 2 smallest numbers can be formed have "2" at the first digit.
so we can say they are 2xx while the rests of two digits is still missing.

Then, we find for the smallest numbers remaining(3,4,5,7,8) for last 2 digits for each number
There is no a special method to solve this question. just trial and error. the other smallest 2 digits numbers are 34 and 57.

so the 2 smallest numbers are 234 and 257. We substract them and get 23.

257 - 234 = 23