Count On and Count Back to Subtract
Key Concepts
- Number line.
- Count on to subtract.
- Count back to subtract.
Introduction
Example 1:
The number line given below indicates all the numbers from 60 to 69.
Fill in the missing numbers in the number line.
Solution:
Example 2:
Solution:
Count On to Subtract
Example 3:
Find 5 – 3.
Solution:
Step 1: Start with the lesser number.
Step 2: Count to 5 to find the difference.
Draw each move as you count.
3, 4, 5
It takes 2 moves to count from 3 to 5.
So, 5 – 3 = 2.
Example 4:
Find 11 – 4.
Solution:
Step 1: Start with the lesser number.
Step 2: Count to 11 to find the difference.
Draw each move as you count.
4, 5, 6, 7, 8, 9, 10, 11
It takes 7 moves to count on from 4 to 11.
So, 11 – 4 = 7.
Count Back to Subtract
Example 5:
Find 5 – 3.
Solution:
Step 1: Start with the more significant number.
Step 2: Count back 3 moves to find the difference.
Count back 3 activities.
5, 4, 3, 2
You landed on 2.
So, 5 – 3 = 2.
Example 6:
Find 11 – 4.
Solution:
Step 1: Start with the more significant number.
Step 2: Count back 4 moves to find the difference.
Count back 4 activities.
11, 10, 9, 8, 7
You landed on 7.
So, 11 – 4 = 7.
Exercise
1. Count on or count back to subtract. Show your work on the number line.
14 – 7 = ?
2. Count on or count back to subtract. Show your work on the number line.
14 – 8 = ?
3. Count on or count back to subtract. Show your work on the number line.
12 – 7 = ?
4. Count on or count back to subtract. Show your work on the number line.
9 – 7 = ?
5. Count on or count back to subtract. Show your work on the number line.
15 – 6 = ?
6. Count on or count back to subtract. Show your work on the number line.
15 – 9 = ?
7. Michael has 19 hens, and he gives 12 hens to his sister. How many hens does he have now?
8. 16 birds are sitting on a tree. 4 birds fly away. How many birds are on the tree now?
What we have learned
- Understand the number line.
- Count on the number line to subtract.
- Count back the number line to subtract.
Concept Summary
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