What is a subtraction table? A Subtraction Table is a visual aid. It is designed to help children learn how to subtract numbers and ease the learning process.
Learning Subtraction after Addition is Ideal. Children from very early ages learn counting. Counting evolves into addition. The logical and easiest step after addition for children is subtraction. Why learn it before multiplication or division? There are a number of reasons:
- Addition is the sum of two or more counted objects.
- Subtraction is simply the difference of two or more counted objects.
- Children more naturally grasp this simple relationship between addition and subtraction than multiplication or division.
- Moreover, multiplication and division have a relationship. Division is the reciprocal of multiplication. The ideal approach is to learn multiplication and division sequentially.
Review the Basics. Let us review a subtraction example. Using the Subtraction Table, subtract seven minus two and get an answer five: 7 – 2 = 5. The intersection of row seven and column two is five; five is the answer. For children starting to learn subtraction, this is easy. They can use their fingers to solve the problem. It is also an excellent introduction to the Subtraction Table. In this example, we looked at the positive answer case. If the row number is greater in value than the column number, the answer to the problem is always positive i.e. greater than or equal to one.
Now let us examine the case where the answer is zero. Using the table, subtract seven minus seven and get an answer zero: 7 – 7 = 0. The intersection of row seven and column seven of the table is zero; zero is the answer. In this example, we looked at the zero answer case. If the row number is equal in value to the column number, the answer to the subtraction problem is always zero.
The last case is the most difficult for children to grasp, the case where the subtraction answer is a negative number. Using the table, subtract seven minus nine and get an answer minus two: 7 – 9 = -2. The intersection of row seven and column nine of a Subtraction Table is minus two; minus two is the answer. For children starting to learn subtraction, this can be a difficult concept. How can there be a negative of something? The best way to address this by a rule: subtract the row number from the column number and put a minus sign in front of the answer. In this example, we looked at the negative answer subtraction case. If the row number is less in value than the column number, the answer to the problem is always negative i.e. less than or equal to minus one.
Where do we begin learning subtraction using the Subtraction Table?
- First, get familiar with the table.
- Start at row number one. Move to column number one. The intersection of row one and column one is the answer: zero.
- Subtract columns one through three from row seven. The answers are 6, 5, and 4 respectively.
- Subtract columns one through eight from row two. The answers are 1, 0, -1, -2, -3, -4, -5, and -6 respectively.
- Let us jump ahead. Now let us increase the level of difficulty. Subtract columns one through twelve from row five. The answers are 4, 3, 2, 1, 0, -1, -2, -3, -4, -5, -6, and -7 respectively.
- If you are doing well so far, try a test. Solve the following problems in your head and then compare your answers to the table: two minus six, nine minus nine, four minus three, ten minus five, and seven minus twelve. The problem answers are 4, 0, -1, -5, and 5 respectively.
If you got four out of five problems correct, create your own tests. Calculate the answer in your head, and check your answer using the Subtraction Table.