1. Math 801A: Mental Math - Subtraction Strategies
Mathematics Essentials
Feb 22nd, 2017

2. Lesson Introduction Today I will...
use mental math and estimation strategies for operations involving integers
apply mental math and estimation strategies in problem situations when appropriate

3. What did we learn/do last class?
Reviewed/learned the “Front- End” and “Make 1, 10s, 100s…” strategies for addition-related mental math.
Worked on the assignment (pg. 5, q. 4).

4. Word Problems/Review
Using the mental math strategies we have discussed, complete q’s 7-10 on pg 6.

5. Important Terms - Review (Addition)
A + B = C
addend + addend = sum

6. Important Terms (Subtraction)
A - B = C
minuend - subtrahend = difference

7. Front-End Strategy
Decompose and perform calculations from left to right.
Practice q’s 1A-D on pg. 7.

8. Make 1, 10s, 100s… Strategy
Make the subtrahend a factor of 1, 10s, 100s… by adding OR subtracting the same quantity from both numbers (Constant Difference).
Round both numbers up or down by the same quantity using 5s, 50s, 500s… as benchmarks.

9. Constant Difference
Similar to borrowing/compensation. What did we do for the Make 1, 10s, 100s… strategy with addition?
Example:
(48+2) + (52-2)
100

10. Constant Difference
Remember: the “net result” should be zero so you don’t change the sum/difference… essentially rearranging the given numbers to make them easier to work with.

11. Constant Difference
With addition we need to add to one term and subtract from the other to make the net result zero.
What about subtraction?

12. Make 1, 10s, 100s… Strategy
Practice q’s 2A-D on pg. 8.

13. Subtract by Counting Up Strategy
Think addition!
Starting at the subtrahend count up to a “nice number” or by tens.

14. Subtract by Counting Up Strategy
Can be done two ways…
Count up to a nice number and adjust at the end
Count up by ten and adjust at the end
Practice q’s 3A-D on pg. 8.

15. Subtraction Strategies
Front-End
Make 1, 10s, 100s…
Subtraction by adding up
Left to right.
Group terms according to place value (e.g. hundreds, tens, ones, tenths) and subtract.
Make the subtrahend an easier number to work with by adding/subtracting then do the SAME to the minuend to ensure a constant difference.
Start with subtrahend.
Add up by 1s or 10s to make “nice numbers” until you reach the minuend.

16. Homework! All four math bootcamp booklets for FRIDAY’s class!
Mental Math subtraction problems are due FRIDAY.