Lesson
5 Traditional Subtraction
Monitoring Progress:
Quiz 1
Traditional Subtraction
Vocabulary
What is traditional subtraction?
We know how traditional addition compares with expanded addition.
Let’s look at these two methods.
Expanded Addition
Traditional Addition
10
55 S 50 5
+ 19
+ 10 9
70 4 = 74
1
55
+ 19
74
We know the advantages and disadvantages of each of these
methods. Traditional addition is more efficient, but it is easier to
make a regrouping mistake. Expanded addition makes it easier to
see regrouping, but it takes longer to do. Now we’ll see how the same
methods compare in subtraction.
Usually we solve problems using traditional subtraction . This is a
shorthand method where we have to remember the value of each digit.
Steps for Using Traditional Subtraction
Step 1
Check to see if we need to regroup.
Note that 4 is less than 9. We need to regroup.
Step 2
Regroup.
Regroup 1 ten to the ones column. Now there
are 5 tens and 14 ones.
Step 3
Subtract.
The difference is 35.
90 Unit 2 • Lesson 5
64
 29
5 14
64
 29
5 14
64
 29
35
traditional
subtraction
Lesson 5
How does regrouping compare in expanded
and traditional subtraction?
The two methods of subtraction we learned are compared below.
Each method has its advantages and disadvantages when it comes
to regrouping.
Expanded Subtraction
• Clearly shows regrouping.
• Shows the value of each digit.
• Takes longer to write all the steps.
Traditional Subtraction
• Shows regrouping in a shorthand way.
• Relies on memory to know the value of each digit.
• Takes less time to write the steps, so it is more efficient.
We want to subtract efficiently. This means working quickly and
accurately. This is why most people use the traditional method of
subtraction. In the lessons to come, we need to be efficient with
computations so that we can focus on other concepts.
Apply Skills
Turn to Interactive Text,
page 63.
Monitoring Progress
Quiz 1
Expanded subtraction
makes regrouping
clear, but traditional
subtraction is more
efficient.
Reinforce Understanding
Use the mBook Study Guide
to review lesson concepts.
Unit 2 • Lesson 5 91
Lesson 5
Homework
Activity 1
Find the difference using traditional subtraction.
1.
78
 39
2.
39
5.
538
 47
3.
62
 25
491
271
 63
6.
208
4.
37
891
 529
362
919
 648
271
Activity 2
Describe what the circled number represents in the problem.
Model
The circled 6 represents what is left
in the tens place when we regroup
one 10 from the tens to the ones. It
has a value of six 10s, or 60.
6 14
74
 48
26
1.
7 14
84
 16
68
2.
4 16
56
 18
38
Activity 3
Find the difference using expanded form. Then write the answer in standard form.
Model
74
70 4
70 4
60 + 10 4
60 10 + 4
 26 S − 20 6 S − 20 6 S −
20 6 S − 20 6
60 14
S − 20 6
40 8 S 40 + 8 = 48
1.
36
 19
2.
64
 25
3.
94
 77
4.
82
 17
3.
495
+ 518
4.
187
+ 717
Activity 4 • Distributed Practice
Add.
1.
679
+ 207
886
92 Unit 2 • Lesson 5
2.
847
+ 319
1,166
1,013
904