Posted: Wednesday, January 22nd, 2014
From time to time, we host ‘special guests’ in the Education.com office: our staff’s children! This past week, we hosted a pair of very studious first graders intent on doing their homework in office each afternoon. Because we’re all charitable and friendly adults, several members of the Education.com staff were coerced into assisting the kids with story tables, practice spelling quizes, and—most terrifying of all—math worksheets.
When they came to us with a long list of problems that required subtraction with regrouping, we struggled with the words to explain the concept to six-year-olds. After a few days (and a few two-digit subtraction with regrouping worksheets), we felt confident that we could guide even the most confused first grader through his math exercises. We wanted to share our process with you in the event that a child needs help learning how to do subtraction with regrouping.
1. Introduce your child to the different parts of the numbers in a subtraction with regrouping problem. Draw a line down the center of the equation, and explain to your child, “We’re going to be working with two different parts of the numbers in this problem. We’re going to be looking at the tens place and the ones place. The tens place is on the left of our line and the ones place is on the right.” Have your child point to the tens place, and then the ones place. Check for understanding.
2. Let your child know that you’re going to be subtracting in the ones place first. Cover the tens place with another piece of paper. Say to your child, “We have a zero and a five, so our problem for the ones place is ‘0 – 5.’ Can we solve the problem ‘0 – 5?’” Your child should respond with a ‘no.’ Continue, “We can’t solve ‘0 – 5’ because 0 is smaller than 5. We need to make 0 a bigger number, so we’re going to regroup.”
3. Uncover the tens place. Tell your child, “Since we need the top number in the ones place to be bigger, we can borrow from the tens place. Let’s borrow one digit from the tens place.” Show your child how you cross out the number in the tens place and replace it with a number one digit less, in this case, 7 becomes 6.
4. Explain to your child, “Since we took one away from the number in the tens place, we can add a one in front of the number in the ones place. If we add a 1 in front of the 0 in the tens place, what number do we have?” Give your child a moment to think about this question, and, if necessary, guide him to realizing that the number in the ones place becomes 10.
5. Use your second piece of paper to cover the tens place again. Ask your child, “Now that we have the equation ‘10 – 5’ in the ones place, what is the answer to that problem?” Your child should respond that the answer is 5. Show him where he should write his answer.
6. Now, use your second piece of paper to cover up the digits in the ones place. Tell your child, “Now, we need to solve the problem in the tens place. Since we borrowed from the number 7, we’re now solving the problem ‘6 – 3.’” Have your child solve the problem and write the answer in the tens place.
7. You’re done! Repeat the process with a different subtraction with regrouping problem, then have your child solve a problem on his own.