A Subtraction AlgorithmA Subtraction Algorithm

Trade FirstTrade First

““The Trade First algorithm The Trade First algorithm resembles resembles the traditional methodthe traditional method of subtraction, of subtraction, except that all the trading is done except that all the trading is done before all the subtraction, before all the subtraction, allowing the allowing the user to concentrateuser to concentrate on one thing at a on one thing at a time.” time.”

This is an easy to learn method that is very efficient. This is an easy to learn method that is very efficient. Vertical linesVertical lines can be used to help the students focus can be used to help the students focus on one column at a time and reduce mistakes. on one column at a time and reduce mistakes.

Based on EM resourcesBased on EM resources

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

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

9 3 2

- 3 5 6

8 13

12 1

2

2 7 6

When subtracting using this algorithm, start by going from left to right.Ask yourself, “Do I have enough to subtract the bottom number from the top in the hundreds column?”

In this problem, 7 - 4 does not require regrouping.

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 regroup.

Now subtract column by column in any order

7 2 5

- 4 9 8

6 12

11 1

5

2 2 7

9 4 2

- 2 8 7

8 14

13 1

2

6 5 5