Meaning and Basic Addition of Whole Numbers for Primary 1

Addition

Performance Objectives

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

1. add two whole numbers from 1 to 3 with sum less than 5;
2. Add two or three whole numbers from 1 to 8 with sum not up to 10;
3. Add two or three numbers from 0 to 9 with sum not greater than 18;
4. Add 2-digit whole numbers with sum not greater than 40 without exchanging or renaming.

What is Addition?

Addition is the process of putting two or more numbers or groups of items together to find a total.

When people add, they are finding out how many items there are in all after joining different groups. The plus sign (+) is used to show addition. The equal sign (=) shows that the numbers on both sides are the same.

Counting Numbers

Counting is an important skill for addition. It means saying numbers in order, like one, two, three, four, and so on. When adding, counting helps to find the total number of items.

For example, if there are 3 oranges and 2 more oranges are added, counting all of them one by one will give the total number of oranges.

Sorting and Grouping Numbers

Before adding, it can be helpful to sort and group items. Sorting means arranging items based on a common feature, like colour, size, or type. Grouping means putting similar items together.

For example, if there are different fruits like oranges, apples, and bananas, sorting them means putting all the oranges together, all the apples together, and all the bananas together. Grouping them helps to count each type easily before adding them up.

Adding Two Whole Numbers (Sum Less Than 5)

This involves putting together small numbers like 1, 2, and 3. The total will always be less than 5.

To add these numbers, count all the items in both groups. For example, if you have 2 oranges and someone gives you 1 more orange, you count all of them to find the total.

Let us look at some examples:

1. $1 + 1 = 2$
2. $1 + 2 = 3$
3. $2 + 1 = 3$
4. $1 + 3 = 4$
5. $3 + 1 = 4$
6. $2 + 2 = 4$

Worked Example 1:

Add 2 and 1.

Solution:

Start with 2 items. Add 1 more item. Count all the items: 1, 2, 3.

$2 + 1 = 3$

Worked Example 2:

Add 1 and 3.

Solution:

Start with 1 item. Add 3 more items. Count all the items: 1, 2, 3, 4.

$1 + 3 = 4$

Adding Two or Three Whole Numbers (Sum Not Up to 10)

This involves adding numbers from 1 to 8. The total sum will not be 10 or more. You can add two or three numbers together.

Using counters or drawing pictures can help to find the total.

Let us look at some examples:

1. $5 + 3 = 8$
2. $7 + 2 = 9$
3. $4 + 1 + 3 = 8$
4. $6 + 2 + 1 = 9$

Worked Example 1:

Add 5 and 3.

Solution:

Count 5 items. Then count 3 more items. Count all the items together: 1, 2, 3, 4, 5, 6, 7, 8.

$5 + 3 = 8$

Worked Example 2:

Add 4, 1, and 3.

Solution:

Count 4 items. Add 1 more item. Then add 3 more items. Count all the items together: 1, 2, 3, 4, 5, 6, 7, 8.

$4 + 1 + 3 = 8$

Adding Two or Three Numbers (Sum Not Greater Than 18)

This involves adding numbers from 0 to 9. The total sum will not be more than 18. This can be done by counting all the items or by counting on from the larger number.

Let us look at some examples:

1. $9 + 9 = 18$
2. $8 + 6 = 14$
3. $5 + 0 = 5$
4. $7 + 4 + 5 = 16$
5. $6 + 8 + 3 = 17$

Worked Example 1:

Add 9 and 7.

Solution:

Start with 9 items. Count 7 more items from 9: 10, 11, 12, 13, 14, 15, 16.

$9 + 7 = 16$

Worked Example 2:

Add 6, 8, and 3.

Solution:

First, add 6 and 8. Start with 8 and count 6 more: 9, 10, 11, 12, 13, 14. So, $6 + 8 = 14$.

Now add 3 to 14. Start with 14 and count 3 more: 15, 16, 17.

$6 + 8 + 3 = 17$

Adding 2-Digit Whole Numbers (Sum Not Greater Than 40, Without Exchanging)

Two-digit numbers have two parts: tens and ones. For example, in the number 23, ‘2’ is in the tens place and ‘3’ is in the ones place.

When adding 2-digit numbers without exchanging (also called without carrying over), always start by adding the numbers in the ones column first. Then, add the numbers in the tens column.

The sum of the numbers in each column must not be 10 or more. The total sum of the two numbers will not be greater than 40.

Let us look at some examples:

Worked Example 1:

Add 12 and 13.

Solution:

First, add the ones:

$2 + 3 = 5$

Then, add the tens:

$1 + 1 = 2$

The total is 25.

$$
\begin{array}{r}
12 \\
+13 \\
\hline
25
\end{array}
$$

Worked Example 2:

Add 21 and 18.

Solution:

First, add the ones:

$1 + 8 = 9$

Then, add the tens:

$2 + 1 = 3$

The total is 39.

$$
\begin{array}{r}
21 \\
+18 \\
\hline
39
\end{array}
$$

Worked Example 3:

Add 30 and 10.

Solution:

First, add the ones:

$0 + 0 = 0$

Then, add the tens:

$3 + 1 = 4$

The total is 40.

$$
\begin{array}{r}
30 \\
+10 \\
\hline
40
\end{array}
$$