Instructions
Today we will explore some special rules for subtraction. In addition, we know that switching the order of numbers doesn't change the answer (for example, 2 + 3 is the same as 3 + 2). Let's see if subtraction works the same way!
Part 1: The Order Rule
Solve the problems in each box. Are the answers the same or different? Circle your choice.
1.
7 - 4 = ______
4 - 7 = ______ (Can you take 7 away from 4?)
Same / Different
2.
10 - 6 = ______
6 - 10 = ______
Same / Different
3.
9 - 2 = ______
2 - 9 = ______
Same / Different
Conclusion: Does the order of the numbers matter in subtraction? Circle one.
Yes / No
Part 2: The Grouping Rule
The parentheses ( ) in a math problem tell you to "Do this part first!" Let's see if changing how we group the numbers changes the final answer in subtraction.
1. Solve this one step-by-step:
(10 - 5) - 2
↓
______ - 2 = ______
10 - (5 - 2)
↓
10 - ______ = ______
Are the final answers the same or different? Same / Different
2. Now try this one:
(15 - 7) - 3 = ______
15 - (7 - 3) = ______
Are the final answers the same or different? Same / Different
Conclusion: Does changing the grouping of the numbers matter in subtraction? Circle one.
Yes / No
Super Subtraction Summary!
Great work! You discovered that subtraction is special.
Unlike addition, the order of the numbers and the way you group them will change the final answer!
Answer Key
Part 1: The Order Rule
1. 7 - 4 = 3; 4 - 7 = Can't do! / Not the same. Circle: Different
2. 10 - 6 = 4; 6 - 10 = Can't do! / Not the same. Circle: Different
3. 9 - 2 = 7; 2 - 9 = Can't do! / Not the same. Circle: Different
Conclusion: Circle: Yes
Part 2: The Grouping Rule
1.
(10 - 5) - 2
↓
5 - 2 = 3
10 - (5 - 2)
↓
10 - 3 = 7
Circle: Different
2.
(15 - 7) - 3 = 5 (because 8 - 3 = 5)
15 - (7 - 3) = 11 (because 15 - 4 = 11)
Circle: Different
Conclusion: Circle: Yes