An alternative subtraction algorithm

1
Trade-First Subtraction

• An alternative subtraction algorithm

2
12
8
12
In order to subtract, the top number must be
larger than the bottom number
13
9 3 2 - 3 5 6
Start by going left to right. Ask yourself, Do I
have enough to take away the bottom number? In
the hundreds column, 9-3 does not need trading.
5
6
7
Move to the tens column. I cannot subtract 5 from
3, so I need to trade.
Move to the ones column. I cannot subtract 6 from
2, so I need to trade.
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 trading.
2
7
2
Move to the tens column. I cannot subtract 9 from
2, so I need to trade.
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!