What is the difference between the greatest whole number a
Nd the least whole number you can make using the digits 3,8,1, and 5?
Use each digit exactly once in each number.

The digits are "worth" more the further they appear to the left. In other words, as I'm sure you know, the right-most digit is the 1's place, followed by the 10's, the 100's, etc. as you move to the left. Hence, if you want to make the greatest possible number with a set of digits, you want the left-most numbers to have the greatest value. Therefore, you should simply write the numbers in decreasing numerical value, and you'll have the greatest possible number. Do the opposite (write them in increasing order), and you'll have the least possible number. Then just subtract the two to find the difference. Couldn't be easier.