Field Elementary School

Subtraction Fact Strategies

Count Back Facts

There are 27 Count Backs facts with -1. -2. and -3. 

When counting back emphasize the first number, pause, then continue counting down.

          Example: 11 – 3:  say, “11, pause, 10, 9, 8.”

 

10 Facts

 

 Subtracting from 10, students use their knowledge of 10 frame addition facts to help them solve these facts.

 

                   10 – 8 = 2  think of 8+2 = 10

 

Zero Finger Facts

The Zero Finger strategy is related to Subtracting from 10. 

When there is a fact such as 13 – 5, the strategy is to cover the 3 in the 13 and think of a 0, so now the fact so then the fact is 10 – 5 = 5.  Next you add back the 3.  Which make the answer 8.  (13 -5 = 8)  This strategy is helpful for any fact that has 2 digits on top.

 

Another example: 15 – 8              

  Think 10 – 8 = 2      Then add back the 5 you covered up.

                              The answer is 7.  15 – 8 = 7

 

Zero Facts

There are 19 Zero facts. 

For Zero facts such as 9 – 9 = 0 think, “Take all, leave none.”     For Zero facts such as 9 – 0 = 9 think, “Take none, leave all.”

Magic 9 Facts

The Magic -9’s strategy uses number patterns.  One strategy is….the answer is one more than the digit in the ones place.  For example, 14 – 9 is 5 (the ones place is 4, so the answer is 5.) 

Another strategy is…..adding the digits of the number being subtracted.  For example,14 – 9, 1+ 4 = 5.  These patterns only work for the magic 9’s. 

 

For a fact like 13 – 4, the “magic” works like this.  If you can add the top two digits and it is the same as the bottom number, the answer is 9.

13 – 4,   1+3 is 4, the answer is 9.  Try it!