Super Easy Subtraction with the Table
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? The reasons
could be because addition is the sum of two or more counted objects and 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.
To
guide our students do subtraction for the first time, a subtraction table may
be helpful. A Subtraction Table is a visual aid that is designed to help
children learn how to subtract numbers and ease the learning process.
Let us review a subtraction example. Using the Subtraction Table, subtract seven
minus two and get an answer five: 9 - 7 = 2. The intersection of row nine and
column seven is two; 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.
How
do we get most out of 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.
