An alternative subtraction algorithm

1
Trade-First Subtraction

• An alternative subtraction algorithm

2
12
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
6
7
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
3
11
Lets 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
7
2
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
4
13
8
12
3
9 4 2 - 2 8 7
Now, do this one on your own.
6
5
5
Let's see if you're right.
Congratulations!
5
9
Last one! This one is tricky!
6
13
10
7 0 3 - 4 6 9
2
4
3
Let's see if you're right.
Congratulations!