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Trade-First Subtraction. An alternative subtraction algorithm . 12. When subtracting using this algorithm, start by going from left to right. 8. 12. 13. 9 3 2 - 3 5 6.

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Presentation Transcript

An alternative subtraction algorithm

Created by Rina Iati, South Western School District, Hanover, PA

When subtracting using this algorithm, start by going from left to right.

8

12

13

9 3 2

- 3 5 6

Ask yourself, “Do I have enough to subtract the bottom number from the top in the hundreds column?” In this problem, 9 - 3 does not require regrouping.

5

7

6

Move to the tens column. I cannot subtract 5 from 3, so I need to regroup.

Move to the ones column. I cannot subtract 6 from 2, so I need to regroup.

Now subtract column by column in any order

Created by Rina Iati, South Western School District, Hanover, PA

Let’s try another one together

6

15

12

7 2 5

- 4 9 8

Start by going left to right. Ask yourself, “Do I have enough to take away the bottom number?” In the hundreds column, 7- 4 does not need regrouping.

2

2

7

Move to the tens column. I cannot subtract 9 from 2, so I need to regroup.

Move to the ones column. I cannot subtract 8 from 5, so I need to trade.

Now subtract column by column in any order

Created by Rina Iati, South Western School District, Hanover, PA

8

12

14

9 4 2

- 2 8 7

Now, do this one on your own.

6

5

5

Let's see if you're right.

Congratulations!

Created by Rina Iati, South Western School District, Hanover, PA

Last one! This one is tricky!

6

13

10

7 0 3

- 4 6 9

2

3

4

Let's see if you're right.

Congratulations!

Created by Rina Iati, South Western School District, Hanover, PA