Teaching Subtraction with Regrouping: Strategies and Examples

The Regrouping Method of Teaching Subtraction

Strategy

Young children seem to learn best when they can see how something works. If you show your child how to do subtraction with regrouping as you write a problem, he can generally grasp the concept. To begin with, use a single piece of standard-sized paper to write the problem. You want room to show the steps as you demonstrate how to solve the problem. Examples for how to do this are given below.

Examples

For both examples listed below, write the problem '43 - 7' in the vertical form with large numerals on a piece of paper. Leave plenty of space between numbers, both horizontally and vertically, for writing the number that is carried and borrowed. You may even want to draw a dotted line between the ones and tens columns.

The first example uses 43 dried beans and four snack-size baggies to demonstrate regrouping. The second example uses marks on paper to visually show how to solve the problem.

Baggies and Beans

1. Ask your child to count out ten beans for each of the four baggies, pointing out that there will be three beans left over. Show that you have four tens and place the four baggies above the written four. Then place the three loose beans above the written three.
2. Ask your child how much 3 - 7 is while pointing to the numbers on the right side of the equation. She may tell you that you can't subtract seven from three because seven is bigger than three. Explain that it's possible, and you will show her how.
3. Open one of the baggies and add the ten beans from it to the three separate beans you already have. Point out that you now only have three bags of beans. Cross out the four in the written problem and write a three to the left of it. Count the loose beans above the ones column, and then write a one in front of the three, giving you 13.
4. Ask your child what 13 - 7 is. If she doesn't know the answer from memory yet, remove seven beans from the group of 13 and count those that remain. Write this remainder of six in the ones column of the answer.
5. Show that you have three bags of beans left, and you are not subtracting anything from them. Then, bring down the three to the answer line so your final answer is 36.

Marks on the Paper

1. To the left of the four in the number 43 that's written on the paper, make four circles with ten dots in each. Point out that you have 40 dots.
2. To the right of the three, put three dots. Ask your child how many dots would remain if you took seven of them away. As above, he may tell you that you can't take seven dots away from three dots.
3. Tell your child that you are going to fix that by moving ten dots from the four and adding them to the three. Cross out one of the circles and draw another circle with ten dots to the right of the three. Also, show that now you only have three circles of ten dots in the tens column, so you cross out the four and write a three in its place.
4. Count the dots to the right of the three. You now have 13 dots there, so write a one in front of the three to make it 13.
5. Subtract as in the previous example.