Sunday, February 17, 2013

Tips to teach children two digit subtraction.

After learning basic subtraction using numbers from 1 to 10, children will learn how to subtract two digit numbers with and without borrowing. This article will explain the procedure to subtract two digit numbers and how to borrow. Parents will be given tips on how to help their children on this topic
Two digit subtraction is done much the same way as two digit addition. Subtract the ones digit numbers first and the tens digit next. For example, if the problem is 65 - 24, do 5 - 4 first, which is 1. Then do 6 - 2, which is 4. The answer is 41. When subtracting money, keep the decimal place in line and subtract the same as in the last problems. For example, $0.75 - 0.41 = $0.34 and $0.66 - 0.04 = $0.62.

But how do we subtract a problem such as 66 - 19? Notice in the previous examples, the second number had a ones digit smaller than the ones digit in the first number. But that is not the case when solving 66 - 19. When subtracting 9 from 6 in the ones place, we get a number less than 0. There are two ways to solve this problem. The first is the method of borrowing.

When borrowing in the previous example, take 1 away from the tens place. That turns the 6 into 5. In essence, we are borrowing 10 and adding it to the number in the ones place. Place the 1 in front of the 6 in the ones place to make it 16. Subtract 9 from 16 to get 7. Then subtract 1 from 5 on the tens place to get 4. The answer is 47.

We can also solve the problem by subtracting 9 from 6. We can use a number line to show how to subtract 9 from 6. Place a dot at 6 and move 9 places to the left. After moving 6 places, we are at 0. You have to move 3 more places so there are negative numbers. The first negative number counting by 1 is -1, then -2, -3 and so on. Doing this, we get 6 - 9 = -3.

Subtract 1 from 6 in the tens place to get 5 and add the 0 to get 50. Next write -3 under the 0 in 50 to get 50 - 3. Subtract to get 47. Notice the answer is the same.

We can subtract 3 two digit numbers by subtracting 2 of them, then subtracting the 3 rd. To solve 99 - 43 - 18, take 99 - 43 = 56. Then take 56 - 18 = 38. You can also subtract 18 from 99 first and then subtract 43 and get the same answer. Take 99 - 18 = 81, and then 81 - 43 = 38.

Tips for parents:
Make up some subtraction problems with borrowing. Allow your child to look at the example problems in this article for the first few problems so he or she can understand the procedures. Then have your child attempt problems without the use of the examples. Also, make up some fun activity type problem such as subtraction problems where you fill in the blank to solve. Another type of activity would be to match answers to subtraction problems with numbers drawn on cars or balloons or blocks. Once your child can consistently solve these types of problems correctly, he or she is ready for basic multiplication.
This article should help children master the concept of subtraction with borrowing and enable parents to help their children accomplish this goal.

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