The natural number 28A9B consists of different numbers and A is not equal to 0. When the number is divided by 9 the remainder is 7 and when it is divided by 5, the remainder is 1. What is A-B=?
If a number is divisible by 5, the last digit should be 0 or 5. And if the remainder is 1, the last digit should be 1 or 6. So B is either 1 or 6.
If a number is divisible ...
This shows how to use principles of natural numbers and divisibility to solve for variables.