After learning how to count and add, children will learn about basic subtraction. Suppose there are 4 blocks on a table. After taking the blocks from the table and putting them on the floor, there are 4 blocks on the floor. Now suppose while playing with the blocks, we put one block back on the table. We are taking away a block from the floor, so instead of having 4 blocks on there floor, there are now 3 blocks on the floor. This is the basic idea of subtraction. We take away objects. Using the illustration below, see that 4 take away 1 is 3. As a math problem, this is written as 4 – 1 = 3. The “-” sign means subtract and the “=” sign means equals.
Subtraction is the reverse of addition. Suppose in the above example, after putting a block on the table, we decide we need that block again. So we pick up the block and add it to the 3 blocks on the floor and there are now 4 blocks on the floor. So as math problems we write 3 + 1 = 4 and going back to 3, we take one away, or subtract to get 4 – 1 = 3. It is also said the subtraction undoes addition and addition undoes subtraction. Here are some more examples of this fact:
5 + 2 = 7 and 7 – 2 = 5
8 + 1 = 9 and 9 – 1 = 8
3 + 5 = 8 and 8 – 5 = 3
2 + 4 = 6 and 6 – 4 = 2
Another way to illustrate addition is with a number line. For the above example, 4 – 1 = 3, we can show this on the line by first putting a dot at 4. When subtracting 1, count 1 number to the left, which gives us the answer of 3.
Tips for parents:
Place a few balls, blocks or other items on the floor. Have your child pick up a certain number of items from the floor and place them on a table. Next, ask your child to write the subtraction problem representing taking away the balls and the answer. For example, if there are 5 balls on the floor and you ask your child to put 3 of them on the table, he or she should write 5 – 3 = 2.
Next have your child illustrate the same problem on a number line. In the above example, your child would place a dot at 5 and move 3 places to the left and place another dot at 2 to illustrate the answer.
You can then reserve the procedure by having your child take the 3 items from the table and put them back on the floor with the other items. This will reinforce the concept of how addition undoes subtraction and subtraction undoes addition.
Continue with examples of this type until your child can consistently answer correctly.
When adding odd number or even numbers the answer is an even number. When adding an odd to an even number, the answer is an odd number. The same is true with subtracting. Look what happens subtracting two even numbers.
10 – 0 = 10, 8 – 0 = 8, 6 – 0 = 6, 4 – 0 = 4, 2 – 0 = 0, 0 – 0 = 0
10 – 2 = 8, 8 – 2 = 6, 6 – 2 = 4, 4 – 2 = 2, 2 – 2 = 0
10 – 4 = 6, 8 – 4 = 4, 6 – 4 = 2, 4 – 4 = 0
10 – 6 = 4, 8 – 6 = 2, 6 – 6 = 0
10 – 8 = 2, 8 – 8 = 0
10 – 10 = 0
The answers are all even numbers. Look what happens when subtracting two odd numbers.
9 – 1 = 8, 7 – 1 = 6, 5 – 1 = 4, 3 – 1 = 2, 1 – 1 = 0
9 – 3 = 6, 7 – 3 = 4, 5 – 3 = 2, 3 – 3 = 0
9 – 5 = 4, 7 – 5 = 2, 5 – 5 = 0
9 – 7 = 2, 7 – 7 = 0
9 – 9 = 0
Again, the answers are all even numbers. Look what happens when subtracting even numbers from odd numbers.
9 – 0 = 9, 7 – 0 = 7, 5 – 0 = 5, 3 – 0 = 3, 1 – 0 = 1
9 – 2 = 7, 7 – 2 = 5, 5 – 2 = 3, 3 – 2 = 1
9 – 4 = 5, 7 – 4 = 3, 5 – 4 = 1
9 – 6 = 3, 7 – 6 = 1
9 – 8 = 1
The answers are all odd numbers. Look what happens when subtracting odd numbers from even numbers.
10 – 1 = 9, 8 – 1 = 7, 6 – 1 = 5, 4 – 1 = 3, 2 – 1 = 1
10 – 3 = 7, 8 – 3 = 5, 6 – 3 = 3, 4 – 3 = 1
10 – 5 = 5, 8 – 5 = 3, 6 – 5 = 1
10 – 7 = 3, 8 – 7 = 1 1
10 – 9 = 1
Again, the answers are all odd numbers.
* Tips for parents:
Buy flashcards with simple subtraction problems such as those above. Have your child recite or write the answers to the problems on the cards.
You can also have them recreate the charts above, subtracting even from even, odd from odd, even from odd and odd from even.
This article should help children with difficulty in basic subtraction and allow parents to get involved with their child’s early math education.
