An alternative subtraction algorithm Created by Rina Iati

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. 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. 12 13 12 - 3 5 6 5 7 6 8 9 3 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 2

Let’s try another one together 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. 11 12 15 - 4 9 8 2 2 7 6 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 Created by Rina Iati, South Western School District, Hanover, PA 5

13 14 12 - 2 8 7 6 5 5 8 9 Now, do this one on your own. Created by Rina Iati, South Western School District, Hanover, PA 4 2

Last one! This one is tricky! 9 10 13 - 4 6 9 2 3 4 6 7 Created by Rina Iati, South Western School District, Hanover, PA 0 3