Using Constant Difference for Subtracting Mixed Numbers

We have been working on a new strategy, constant difference, for subtracting mixed numbers in which the fractional part of the minuend is less than the fractional part of the subtrahend. In the standard algoritm, you would have to regroup from the wholes and make an improper fraction in the minuend in order to subtract the fraction. In constant difference, the goal is to add an amount to the subtrahend (the amount being subtracted) in order to make it a whole number. Then you add the same amount to the minuend (the amount you are subtracting from) in order to keep the difference constant (the same). You now have a new minuend and a new subtrahend, and a much simpler equation to solve. Below is an example taken from class: