Largest two-digit number

 What is the largest two-digit number that is divisible by 5 and whose digits differ by 3?

 * Using reasoned guess and check is the easiest way to solve this problem

Let's start with the largest 2-digit number divisible by 5  - 95. The difference between the digits in 95 is 4, this doesn't fit our second criteria. 

Moving on to the next largest number divisible by 5 - 90. The difference between these 2 digits is 9 which again does not fit our criteria. 

Now let's try 85. The difference between the digits is 3! 

85 is the largest two-digit number that is both divisible by 5 and its digits differ by 3.

Because we started with 95 (the absolute largest 2-digit number divisible by 5) and worked our way down, we can ensure that 85 is indeed the LARGEST number that fits these criteria. 

Answer: 85