Meaning and Basic Subtraction of Whole Numbers for Primary 1

Meaning and Basic Subtraction of Whole Numbers for Primary 1

Performance Objectives

By the end of the lesson, students should be able to:

1. subtract from whole numbers not greater than 9;
2. subtract from whole numbers not greater than 18.

What is Subtraction?

Subtraction means taking away a part from a whole group of things. When some items are removed from a collection, fewer items are left. Subtraction helps to find out how many items remain.

Imagine a child has a certain number of sweets. If the child eats some of the sweets, the number of sweets left will be less than the original number. This action of taking away is called subtraction.

The sign for subtraction is the minus sign, which looks like this: $-$ .

When we see the minus sign between two numbers, it tells us to take the second number away from the first number.

Counting and Grouping for Subtraction

Before subtracting, it is important to count the total number of items in a group. This helps to know the starting number. After taking some items away, the remaining items are counted to find the answer.

Grouping helps to see the total number of items clearly. When items are grouped, it is easier to take away a specific number of items and then count what is left.

Subtracting Numbers Up to 9

Subtraction can be done using concrete objects like fingers, counters, oranges, or pencils. This helps to see the numbers being taken away.

Using Counters to Subtract

Counters are small objects that can be used to represent numbers. They make it easy to take away and count what is left.

Let us try an example:

Example 1: Subtract 3 from 7.

The procedure involves the following steps:

1. Count out 7 counters and place them in a group.
2. Take away 3 counters from the group.
3. Count the counters that are left.

There are 4 counters left. So, $7 – 3 = 4$.

Example 2: Subtract 2 from 5.

The procedure involves the following steps:

1. Count out 5 counters.
2. Take away 2 counters.
3. Count the remaining counters.

There are 3 counters left. So, $5 – 2 = 3$.

Using Fingers to Subtract

Fingers are useful tools for subtraction, especially for smaller numbers.

Let us try an example:

Example 3: Subtract 4 from 8.

The procedure involves the following steps:

1. Hold up 8 fingers.
2. Fold down 4 of those fingers.
3. Count the fingers that are still standing up.

There are 4 fingers standing up. So, $8 – 4 = 4$.

Using Drawings to Subtract

Drawing pictures can also help with subtraction. Draw the total number of items, then cross out the number being taken away.

Let us try an example:

Example 4: Subtract 1 from 6.

The procedure involves the following steps:

1. Draw 6 circles.
2. Cross out 1 circle.
3. Count the circles that are not crossed out.

There are 5 circles left. So, $6 – 1 = 5$.

Subtracting Numbers Up to 18

The same methods of using concrete objects, fingers, or drawings can be used for larger numbers, up to 18.

Using Objects to Subtract Up to 18

For larger numbers, more counters or objects like oranges and pencils can be used.

Example 5: Subtract 5 from 12.

The procedure involves the following steps:

1. Gather 12 oranges.
2. Take away 5 oranges.
3. Count the oranges that are left.

There are 7 oranges left. So, $12 – 5 = 7$.

Example 6: Subtract 6 from 15.

The procedure involves the following steps:

1. Count out 15 pencils.
2. Take away 6 pencils.
3. Count the pencils that are left.

There are 9 pencils left. So, $15 – 6 = 9$.

Using a Number Line to Subtract

A number line can also be used to subtract. Start at the first number and count backwards the number of steps to be subtracted.

Example 7: Subtract 4 from 10.

The procedure involves the following steps:

1. Find the number 10 on the number line.
2. Move 4 steps backwards (to the left) from 10.
3. The number where you land is the answer.

Moving 4 steps backwards from 10 lands on 6. So, $10 – 4 = 6$.

Example 8: Subtract 7 from 18.

The procedure involves the following steps:

1. Find the number 18 on the number line.
2. Move 7 steps backwards (to the left) from 18.
3. The number where you land is the answer.

Moving 7 steps backwards from 18 lands on 11. So, $18 – 7 = 11$.

Practical Activity: Subtracting with Fingers and Toes

This activity helps to understand subtraction using parts of the body.

The required materials are:

1. Your own fingers and toes.

The procedure involves the following steps:

1. Count all the fingers on both hands. There are 10 fingers.
2. Count all the toes on both feet. There are 10 toes.
3. Add the total number of fingers and toes together. This is $10 + 10 = 20$.
4. Now, subtract the number of fingers on one hand from the total number of fingers and toes.
5. The number of fingers on one hand is 5.
6. So, subtract 5 from 20.

To subtract 5 from 20:

1. Imagine 20 items.
2. Take away 5 items.
3. Count how many are left.

The calculation is $20 – 5 = 15$.

There are 15 fingers and toes left after taking away the fingers from one hand.