Subtraction (whole numbers)

Once students learn how to subtract with regrouping, they can apply those skills to numbers of any size!  For more on regrouping (how and why it works), see lesson on Subtraction (with Regrouping, 2-1 and 2-2 digits).

The first step in subtracting multi-digit numbers is setting the problem up vertically, making sure that the place values are lined up (ones to ones, tens to tens, etc).

Once students have mastered the subtraction facts and learned to stack and subtract multi-digit numbers, it's time to teach them about subtraction with regrouping (or subtraction with borrowing).  It's important that students have some understanding of why and how they are regrouping (they'll need another version of the concept later, when they start working with fractions), but this concept is a difficult one and it's ok to teach it in stages (and not have the students fully understand every part as they go along).

Subtraction is almost always a little more complicated than addition for students. But, it's important, when teaching addition and subtraction to emphasize the relationship between the two process.  Subtraction can be tricky -- but it's not more difficult than addition.  And the rules are much the same.

To that end, make sure a student is comfortable with multi-digit addition (including setting a problem up vertically) before you start subtraction.  Then you can refer to the addition processes as you teach subtraction.

We also subtract all the time, often without thinking about it.  Someone has 5 pieces of candy and then someone takes two, "Hey, I only have 3 left!"  But, teaching subtraction can be a little trickier than teaching addition.