SUBTRACTION

 

Subtraction is the same as TAKE-AWAY. When the number you are subtracting is small, you can just count backwards:

 

10-2: Think 10, 9, 8

7-3: Think 7, 6, 5, 4

12 - 1: Think 12, 11

 

When the number being subtracted is big, you want to count the other way.

 

10-8: Think how many MORE do I need to get from 8 to 10: 2 more

9-6: Think how many MORE do I need to get from 6 to 9: 3 more

 

When the top number is bigger than 10, we will use the BUILD TO 10 strategy.

 

14

-7

For each number, we need to figure out how far each number is away from 10.

For our 14, the answer is EASY - as we did in the previous section we know that 10 + 4 = 14, in fact it will just be the second digit of the number: 4.

For our 7, we will use a quick and easy number chart to find out:

1

2

3

4

5

9

8

7

6

5

 

To make this table, write the numbers 1 through 5. Below the 5, write another 5 and then writing to the LEFT, continue to 9. Each pair should add to 10 if you did it right. So, if we want to find out how far 7 is from 10, we look on the chart for it's partner: 3.

Once we find the distance from 10 for both numbers, we add those two numbers together: 4 + 3 = 7 and that is our answers.

 

Sometimes it is easy to remember: Copy (the ones digit), Partner (use the table), and Add.

 

Examples: Note that the first number is just copied from the ones place, the second number is the partner from the table, then I add.

 

13

-7

 

3

+3

6

15

-8

 

5

+2

7

 

14

-6

 

4

+4

8

 

14

-5

 

4

+5

9

 

 

Let's do it one step at a time together:

 

First how far from 10 are these numbers:

 

13 Answer

16 Answer

17 Answer

12 Answer

19 Answer

18 Answer

11 Answer

14 Answer

15 Answer

 

Use the chart to figure out how far these numbers are from 10?

 

2 Answer

6 Answer

5 Answer

9 Answer

7 Answer

8 Answer

1 Answer

3 Answer

4 Answer

 

Now to convert from a subtraction problem to an addition problem - build each to 10 and add the two numbers:

 

1. 14 - 7 Answer

2. 15- 9 Answer

3. 16 - 8 Answer

4. 12 - 5 Answer

5. 15- 7 Answer

6. 13 - 6 Answer

7. 17 - 9 Answer

8. 16 - 7 Answer

9. 14 - 6 Answer

10. 13 - 8 Answer

 


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