Count Back to Subtract in a Number Line

Introduction:

Count Back to Subtract.

We can use the number line to help to count back to subtract.

Example 1:

5 – 3= ____.

If I start at 5 and count back 3, I end at 2.

5,4,3, 2

5 – 3 = 2            

Example 2:

7 – 0 = ______.        

When we subtract 0,

If I start at 7 and don’t count back any, I stay at 7.

7 – 0 = 7

Count Back to Subtract Examples:

Example 1:

Count back to complete subtraction facts.

Sol:

Start at 8.

When we subtract 3 by counting back 3,

8, 7, 6, 5

End at 5.

So, 8 – 3 = 5

Example 2:

Diana had 7 toffees. She gave 5 toffees to her friend. How many toffees left with her?

Sol:

Total number of toffees with Diana = 7

Number of toffees she gave to her friend = 5

The number of toffees left with Diana = 7 – 5

Start at 7 and count back 5.

7 – 5 = 2

So, 2 toffees left with Diana.

Example 3:

There were 6 boats tied up. 4 of the boats sailed away. How many were left?

Sol:

Total number of boats tied up = 6

Number of boats sailed away = 4

The number of boats left = 6 – 4

Start at 6 and count back 4.

6 – 4 = 2

So, 2 boats were left.

Exercise

1. Count back to complete subtraction fact.

2. Count back to subtract using the number line.

3. Subtract.

4. With the help of number line 7 – 4 = ____.

5. Select the correct one.

10 – 5 = ____

6. Count back to complete the subtraction fact 8 – 6 = ?

7. Tom sees  10 birds in a farm. He scares 6 of them and then they flew away. How many left?

8. Leo has 4 mints. He eats 2 mints. How  many mints does Leo have now?

9.There are 10 students in Grade 1. 6 of them are girls. How many boys are there in Grade 1?

10. Find the value if we take away 1 from 3.

Concept Map:

What We Have Learned

• Count back to subtract
• Subtraction with the help of a number line
• Count back to solve the subtraction problem