Objective – Make equivalent fractions with sums of fractions with like denominators.
Clock Fractions and Common Denominators · a clock face to add and subtract fractions. Remind...
Transcript of Clock Fractions and Common Denominators · a clock face to add and subtract fractions. Remind...
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Lesson 6�9 423
Advance PreparationFor Part 1, display the Multiplication Table Poster on the board or elsewhere for student use. When you
use the Everyday Mathematics posters with English language learners, display either the English version
only or both English and Spanish versions simultaneously; do not display the Spanish version only.
Teacher’s Reference Manual, Grades 4–6 pp. 141, 142, 242, 243
Clock Fractions andCommon Denominators
Objective To provide additional references for fraction concepts.
Key Concepts and Skills• Find common denominators.
[Number and Numeration Goal 5]
• Use clock models and pencil-and-paper
algorithms to add and subtract fractions.
[Operations and Computation Goal 4]
• Use benchmarks to estimate sums and
differences.
[Operations and Computation Goal 6]
Key ActivitiesStudents use a clock face to find equivalent
fractions and to model addition and
subtraction of fractions. They use the
multiplication rule, a multiplication table, and
reference lists to find common denominators.
Ongoing Assessment: Recognizing Student Achievement Use journal page 194. [Operations and Computation Goal 4]
Key Vocabularycommon denominator � unlike denominators
MaterialsMath Journal 1, pp. 194–197
Student Reference Book, p. 401
Study Link 6�8
Math Masters, p. 177
Multiplication Table Poster � demonstration
clock
Playing Fraction CaptureMath Journal 1, p. 198
Math Masters, p. 460
per partnership: 2 six-sided dice
Students practice comparing fractions
and finding equivalent fractions.
Math Boxes 6�9Math Journal 1, p. 199
Students practice and maintain skills
through Math Box problems.
Study Link 6�9Math Masters, p. 178
Students practice and maintain skills
through Study Link activities.
ENRICHMENTModeling Fractions with a Military ClockMath Masters, p. 179
Students apply the clock model to a different
unit by using military time.
EXTRA PRACTICE
Writing Elapsed Time Number StoriesMath Masters, p. 180
Students write a number story using fractions
to represent elapsed time.
Teaching the Lesson Ongoing Learning & Practice
132
4
Differentiation Options
��������
eToolkitePresentations Interactive Teacher’s
Lesson Guide
Algorithms Practice
EM FactsWorkshop Game™
AssessmentManagement
Family Letters
CurriculumFocal Points
Common Core State Standards
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Clock FractionsLESSON
6�9
Date Time
Part 1: Math Message
The numbers on a clock face divide one hour into
twelfths. Each �112� of an hour is 5 minutes.
How many minutes does each of the following fractions and mixed
numbers represent? The first one has been done for you.
1. �112� hr � min 2. �
152� hr � min 3. �
12
� hr � min
4. �13
� hr � min 5. �14
� hr � min 6. �16
� hr � min
Part 2
Using the clock face, fill in the missing numbers. The first one has been done for you.
7. �14
� hr � hr 8. �182� hr � hr 9. �
13
� hr � hr
10. hr � �56
� hr 11. hr � �192� hr 12. �
122� hr � hr
13. 1�12
� hr � hr 14. �53
� hr � hr 15. �142� hr � hr
Part 3
Use clock fractions, if helpful, to solve these problems. Write each answer as a fraction.
Example: �34
� � �13
� � ?
Think: 45 minutes � 20 minutes � 25 minutes
So �34
� � �13
� � �152�
16. �152� � �
132� � 17. �
34
� � �24
� � 18. �1112� � �
132� �
19. 1 � �23
� � 20. �54
� � �24
� � 21. �23
� � �16
� �
22. �14
� � �13
� � 23. �13
� � �14
� � 24. �56
� � �34
� �
101520
30255
312
1012
64
2012
16
32
43
31
62
�1
8
2�, or �
2
3� �
5
4�, or 1�
1
4� �
1
8
2�, or �
2
3�
�1
3�
�1
7
2� �
1
1
2� �
1
1
2�
�3
4� �
5
6�
Rule
hour
Whole
�
Math Journal 1, p. 194
Student Page
424 Unit 6 Using Data; Addition and Subtraction of Fractions
Getting Started
1 Teaching the Lesson
▶ Math Message Follow-Up WHOLE-CLASSDISCUSSION
(Math Journal 1, p. 194)
Review the answers to Part 1 with the class. You might want to pose a few additional easy problems that have mixed numbers or fractions greater than 1. Suggestions:
● How many minutes are in 2 1 _ 2 hours? 150 min
● In 5 _ 2 hours? 150 min
● In 5 _ 4 hours? 75 min
● 3 _ 2 hours is equivalent to how many minutes? 90 min
▶ Using a Clock to Add and PARTNER ACTIVITY
Subtract Fractions(Math Journal 1, p. 194)
Make sure students understand that they may use the clock model to help them answer the problems on the journal page. At times, students might want to “think minutes,” as in the example for Part 3. At other times, students might want to look at the clock face divided into twelfths. Using a demonstration clock, work several of the problems in Part 2 with the class before students work in partnerships. Assign the remainder of the journal page.
Ongoing Assessment: Journal
Page 194 �Problems 16–24Recognizing Student Achievement
Use journal page 194, Problems 16–24 to assess students’ ability to use a
visual model to add and subtract fractions with unlike denominators. Students
are making adequate progress if they correctly solve Problems 16–24.
[Operations and Computation Goal 4]
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Math MessageComplete Part 1 on journal page 194.
Study Link 6�8 Follow-UpHave partners compare answers and resolve differences.
Mental Math and Reflexes Fraction addition and subtraction: Write the problems on the board, and have students estimate using benchmarks and then solve. Students use the estimate to assess the reasonableness of the answers.
7
_ 8 + 2
1
_ 4 = ? 3
1
_ 8
3 5
_ 8 - 1
3
_ 4 = ? 1
7
_ 8
2 1
_ 4 + 2
1
_ 2 + 1
1
_ 4 = ? 6
1 5
_ 8 + 1
1
_ 16
+ 3 3
_ 4 = ? 6
7
_ 16
6 1
_ 2 - 4 + 2
1
_ 4 = ? 4
3
_ 4
4 3
_ 8 + 2 - 1
3
_ 4 + 1
1
_ 2 = ? 6
1
_ 8
NOTE Working with elapsed time can
provide students with more practice using
a clock face to add and subtract fractions.
Remind students that elapsed time is the time
that passes between a given starting and
ending time. Give them various problems that
involve finding elapsed time and then adding
or subtracting the amounts. Ask students to
give the elapsed time in minutes and then in
fractions of an hour. They can then use the
clock face to add or subtract.
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Number Strip FractionsLESSON
6�9
Date Time
Name the strips that you used for the numerator and denominator. Then list the
fractions formed by the two strips. Sample answers:
Problem 1
Strip Fractions List
Name
Numerator:
Denominator:
Problem 2
Strip Fractions List
Name
Numerator:
Denominator:
Problem 3
Strip Fractions List
Name
Numerator:
Denominator:
Problem 4
Explain how you can use a multiplication table to find equivalent fractions for �2
9
7�.
the numbers in the 3 row.
other fractions made by the numbers in the 1 row that correspond to
and the 3 row has 27 for the denominator. I can then list the
the rows for those numbers. The 1 row has 9 for the numerator,
I can look for a column that has both 9 and 27. Then I can find
3
410
97
1
�7
9�, �
1
1
4
8�, �
2
2
1
7�, �
2
3
8
6�, �
3
4
5
5�, �
4
5
2
4�, �
4
6
9
3�, �
5
7
6
2�, �
6
8
3
1�, �
7
9
0
0�
�1
4
0�, �
2
8
0�, �
3
1
0
2�, �
4
1
0
6�, �
5
2
0
0�, �
6
2
0
4�, �
7
2
0
8�, �
8
3
0
2�, �
9
3
0
6�, �
1
4
0
0
0�
�3
1�, �
6
2�, �
9
3�, �1
42�, �
1
5
5�, �
1
6
8�, �
2
7
1�, �
2
8
4�, �
2
9
7�, �
3
1
0
0�
Math Journal 1, p. 195
Student Page
Adjusting the Activity
Lesson 6�9 425
▶ Discussing Strategies for WHOLE-CLASSDISCUSSION
Adding and Subtracting Fractions(Math Journal 1, p. 194)
Discuss students’ solutions to Part 3. Expect that some students converted most fractions to minutes, did the operation, and then converted the answer in minutes back to a fraction. Others may have converted all fractions to twelfths and found the answer without any reference to the clock or time.
Pose fraction problems with denominators of 30 and 60.
Suggestions follow:
• 3
_ 4 +
5
_ 60
50
_ 60
, or 5
_ 6 •
18
_ 30
+ 1
_ 3 28
_ 30
, or 14
_ 15
• 5
_ 12
+ 25
_ 60
50
_ 60
, or 5
_ 6
A U D I T O R Y � K I N E S T H E T I C � T A C T I L E � V I S U A L
NOTE A clock face is a convenient model for fraction operations involving
halves, thirds, fourths, fifths, sixths, twelfths, and even thirtieths and sixtieths. The
link between fractions and their equivalents in minutes allows students to add and
subtract fractions with unlike denominators without rewriting the fractions with a
common denominator.
▶ Using a Multiplication Table
WHOLE-CLASS ACTIVITY
to Explore Equivalent Fractions(Math Journal 1, p. 195; Math Masters, p. 177)
Any two rows of a multiplication table can be used to form equivalent fractions. Display the Multiplication Table Poster on the board. Ask partners to cut the strips from Math Masters, page 177 and place them in the middle of their workspace.
� Each student takes one strip. Ask students to make true statements about the numbers on their strip. The numbers are multiples of the first number on the strip; the numbers have a common factor. Tell them that a strip can be named by its smallest number, for example, the “4 strip.”
� One partner is “numerators” and the other is “denominators.” Partners then match their strips, laying the numerator strip above the denominator strip. Tell students that the columns form fractions.
� For Problem 1, on journal page 195, ask students to write down the strip names and then list all of the fractions formed by the matches.
� Partners then take two different strips and repeat this process for Problems 2 and 3. Each strip should be used only once.
Circulate and assist.
Ask students what they notice about their lists of fractions. The numerators and denominators are multiples of the numbers in the first column; the fractions are equivalent.
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Using a Common DenominatorLESSON
6�9
Date Time
Study the examples. Then work the problems below in the same way.
1. �23� � �
29� � ?
Unlike CommonDenominators Denominators
�23�
� �29�
3. �13� � �
25� � ?
Unlike CommonDenominators Denominators
�13�
� �25�
�34� � �1
92�
Unlike CommonDenominators Denominators
�23� �
46�
� �16� � �
16�
Unlike CommonDenominators Denominators
�56� �
1102�
� �34� � �1
92�
Example 1: �23� � �
16� � ? Example 2: �
56� � �
34� � ?
�56� �1
12�
�23� � �
46� �
56� � �
1102�
�56� � �
1158�
�69�
�29�
�89�
�23� � �
69�
�13� � �1
55�
�25� � �1
65�
�155�
�165�
�1115�
�
�
2. �1136� � �
34� � ?
Unlike CommonDenominators Denominators
�1136�
� �34�
4. �56� � �
49� � ?
Unlike CommonDenominators Denominators
�56�
� �49�
�49� � �1
88�
�34� � �
1126�
�1136�
�1126�
�116�
�
�1158�
�188�
�178�
�
Math Journal 1, p. 196
Student Page
426 Unit 6 Using Data; Addition and Subtraction of Fractions
Ask volunteers to match two of their remaining strips and write the fraction from the first column on the board. Use these fractions to demonstrate the multiplication rule. Example:
4 _ 9 = 4 ∗ 2 _ 9 ∗ 2 = 8 _ 18
Ask students to use the appropriate strips to give another equivalent fraction for 4 _ 9 . Then ask a volunteer to write the number model for this change using the multiplication rule. Sample response: 32 _ 72 = 4 ∗ 8 _ 9 ∗ 8
Refer students to the Multiplication Table Poster. Explain that for any two rows, the equivalent fractions are the result of multiplying the fraction in the first column by another name for 1, such as 2 _ 2 or 8 _ 8 , depending on the column. So the second column is the result of multiplying by 2 _ 2 , the third column is the result of multiplying by 3 _ 3 , and so on.
▶ Using a Common Denominator PARTNER ACTIVITY
(Math Journal 1, pp. 196 and 197; Student Reference
Book, p. 401)
Algebraic Thinking Introduce the next activity by discussing the following points:
● It is easy to add or subtract fractions if they have the same denominator, usually called a common denominator. To support English language learners, discuss the meaning of common in this mathematical context.
● One way to add or subtract fractions with different denominators, usually called unlike denominators, is to rewrite the fractions with a common denominator.
● One way to find common denominators is to use the multiplication rule (or the division rule) for finding equivalent fractions. Ask volunteers to express the rules with variables. a _ b = a ∗ n _ b ∗ n ; a _ b = a ÷ n _ b ÷ n
Have students look at Example 1 and Example 2 at the top of Math Journal 1, page 196. Ask: How could you use benchmarks to estimate the solution to each problem? Sample answer: For Problem 1, I know that 2 _ 3 is greater than 1 _ 2 and 1 _ 6 is less than 1 _ 2 , so theanswer will be close to 1. For Problem 2, I know that 5 _ 6 and 3 _ 4 are both close to 1, so my answer will be close to zero.
NOTE Some students may realize that 1 _ 6 is less than 1
_ 3 and conclude that the
answer will be less than 1.
Then work through the examples to illustrate the use of the multiplication rule to find common denominators. Pose one or two similar problems as needed.
ELL
Adjusting the ActivityRefer students to the Equivalent
Fractions, Decimals, and Percents table on
Student Reference Book, page 401. Ask
students to describe the similarities and
differences between the structure of this
table and their work with multiplication table
number strips. 1 row of the table is similar
to two number strips; the table shows the
equivalent decimals and percents for the
fractions.
A U D I T O R Y � K I N E S T H E T I C � T A C T I L E � V I S U A L
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Math Boxes LESSON
6�9
Date Time
5. Measure each line segment to the nearest�18� in.
a.
in.
b.
in.
1. In the figure below, write the correctfraction in each of the smaller regions.Check to see that the fractional parts addup to 1.
3. Esther did 5 standing jumps. Her longestjump was 50 in. Could her average jumpbe 53 in.?
Create a data set for Esther’s jumps thatcould have this average.51, 52, 53, 54, 55
No
4. Measure the length and width of each of thefollowing objects to the nearest centimeter.
a. pinkie finger
length: ______ cm
width: ______ cm
c. notebook
length: ______ cm
width: ______ cm
6. Rename each fraction as a mixed numberor a whole number.
a. �559� �
b. �8181� �
c. �1270
� �
d. �944� �
e. �1062
� � 17
8
2.
Estimate the measure of �M:
The measure of �M is about .37°
14
12
116
316
M
b. pencil
length: ______ cm
width: ______ cm
2�28�, or 2�
14�
1�18�
11�45�
17�17�
23 �24�, or 23 �
12�
Answers vary.
Answers vary.
75
121
183
204
183
62 63
Math Journal 1, p. 199
Student Page
Using a Common Denominator continuedLESSON
6 �9
Date Time
5. �142� � �
32� � ?
Unlike CommonDenominators Denominators
�142�
7. A piece of ribbon is 7�12� in. long. If a piece
2�136� in. long is cut off, how long is the remaining piece? in.
Write a number sentence to show how you solved the problem.
8. Three boards are glued together. The diagram below shows the thickness of each board. What is the total thickness of the three boards? in.
Write a number sentence to show how you solved the problem.
5�156�
7�186� � 2�1
36� � 5�1
56�
3�58� � �
48� � 2�
68� � 6�
78�
3 85
21 2 4
3" " "
6�78�
6. 1�116� � �
38� � ?
Unlike CommonDenominators Denominators
1�116�
� �38�
�142�
�64��
�1176�
�166�
�32� � �
64�
1�116� � �
1176�
�38� � �1
66�
�148�, or 4�
12�
� �32�
�1116�
�
Math Journal 1, p. 197
Student Page
Lesson 6�9 427
In addition to using the multiplication rule to find equivalent fractions, students can also refer to the Table of Equivalent Fractions, Decimals, and Percents on page 401 of the Student Reference Book.
Assign journal pages 196 and 197. Remind students of the importance of using benchmarks to estimate the solution and then assess the reasonableness of their answers. Students may choose to solve Problems 7 and 8 by finding a common denominator.
NOTE In Problems 1, 2, 5, 6, 7, and 8, on journal pages 196 and 197, the
common denominator is the same as one of the original denominators. In
Problems 3 and 4, the common denominator is different from both of the
original denominators.
2 Ongoing Learning & Practice
▶ Playing Fraction Capture PARTNER ACTIVITY
(Math Journal 1, p. 198; Math Masters, p. 460)
Players roll dice, form fractions, and claim corresponding sections of squares. The rules are on Math Journal 1, page 198, and the gameboard is on Math Masters, page 460. Remind students of the importance of using the benchmark fraction of 1 _ 2 when playing this game.
▶ Math Boxes 6�9
INDEPENDENT ACTIVITY
(Math Journal 1, p. 199)
Mixed Practice Math Boxes in this lesson are paired with Math Boxes in Lesson 6-6. The skill in Problem 6 previews Unit 7 content.
Writing/Reasoning Have students write a response to the following: Explain your answer to the question in Problem 3 and how you chose the values for the data set.
Because the average cannot be greater than the maximum in the data set, 53 inches cannot be Esther’s average since 50 is the maximum number. I chose 5 numbers for the data set that could be added together and divided by 5 so that the average would equal 53.
▶ Study Link 6�9
INDEPENDENT ACTIVITY
(Math Masters, p. 178)
Home Connection Students solve problems similar to those on journal pages 196 and 197. This page reinforces the idea that a common denominator can be determined by finding fractions equivalent to the given fractions.
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Multiplication Rule
To find a fraction equivalent to a given fraction,
multiply the numerator and the denominator
of the fraction by the same number.
STUDY LINK
6�9 Adding and Subtracting Fractions
Name Date Time
�ab� � �
ab
º
º
nn�
Example 1: �4
9� � �
1
3� � ?
�1
3� � �
2
6� � �
3
9� � �
1
4
2� � �
1
5
5� � �
1
6
8� � ...
9 is a common denominator.
�4
9� � �
1
3� � �
4
9� � �
3
9� � �
1
9�
Find a common denominator. Then add or subtract.
1. �2
3� � �
4
5� � 2. �
8
9� � �
5
6� � 3. �
3
4� � 1�
1
2� �
4. Lisa was 4 feet 10�1
2� inches tall at the end of fifth grade. During the year, she
had grown 2�3
4� inches. How tall was Lisa at the start of fifth grade?
feet in.
5. Bill was baking two different kinds of bread. One recipe called for 3�1
2� cups of
flour. The other called for 2�1
3� cups of flour. How much flour did Bill need in all?
cups
4
2�14
��118�1�
175�
Example 2: �5
8� � �
2
5� � ?
�5
8� � �
1
1
0
6� � �
1
2
5
4� � �
2
3
0
2� � �
2
4
5
0� � �
3
4
0
8� � ...
�2
5� � �
1
4
0� � �
1
6
5� � �
2
8
0� � �
1
2
0
5� � �
1
3
2
0� � �
1
3
4
5� � �
1
4
6
0� � �
1
4
8
5� � ...
Both fractions can be rewritten with the
common denominator 40.
�5
8� � �
2
5� � �
2
4
5
0� � �
1
4
6
0� � �
4
4
1
0�, or 1�
4
1
0�
�23
� � �1105� �
8
9� � �
1168� 1�
12
� � �3
2� � �
64
�
�45
� � �1125� �
56
� � �1158� �
34
� � �64
� � �94
�, or 2�14
�
�1105� � �
1125� � �
2125�, �
1168� � �
1158� � �
118�
or 1�175�
5�56
�
6568–71
7�34
�
Math Masters, p. 178
Study Link Master
LESSON
6�9
Name Date Time
Fractions in Military Time
On a military clock, the whole is 1 day or 24 hours. �2
1
4� is one hour. The time
shown on this clock face is 08:14:42 (8 hours, 14 minutes, and 42 seconds).
Using the clock face, write the fractions as days, hours, and minutes. The first
one has been done for you.
1. �2
2
4� �
1of a day � 2 hours � minutes
2. �1
2
8
4� � of a day � hours � minutes
3. �1
2
0
4� � of a day � hours � minutes
4. �1
2� hour � of a day
5. Explain how you found your answer for Problem 4.
Sample answer: �12
� hour is equal to 30 minutes.
48
1
6001012
5
1,080184
3
12012
00
20
16
12
08
04
2322
21
19
18
17
1514
13 1110
09
07
06
05
0302
01
055
50
40
3530
25
20
15
10
5
45
Rule
day
Whole
�1,
34040� � �
1344� � �
418�.
In one day, there are 1,440 minutes, so
Math Masters, p. 179
Teaching Master Teaching Master
LESSON
6�9
Name Date Time
Writing Elapsed-Time Number Stories
The numbers on a clock face divide one hour into twelfths. Each �1
1
2� of an hour is
5 minutes.
Use fractions to represent amounts of elapsed time and write a number story for a
partner to solve.
Example:
Maria started her piano practice at 3:15. She practiced for �1
8
2� of an hour. At what time did
she finish practicing?
Think: �1
1
2� hour � 5 minutes; �
1
8
2� hour is 8 � 5, or 40 minutes; 40 minutes more than 3:15 is 3:55.
Maria finished practicing at 3:55.
Your Elapsed-Time Number Story:
Answers vary.
Your Partner’s Solution:
Answers vary.
Explain your answer.
Answers vary.
12 12
3
4567
8
9
1011
Rule
hour
Whole
Math Masters, p. 180
428 Unit 6 Using Data; Addition and Subtraction of Fractions
3 Differentiation Options
ENRICHMENT PARTNER ACTIVITY
▶ Modeling Fractions with a 15–30 Min
Military Clock(Math Masters, p. 179)
To apply students’ understanding of the fractional units on a 12-hour clock face, have students use a 24-hour military clock face model to add, subtract, and find
equivalent fractions. When they have finished the page, have students describe similarities and differences between using the 12-hour clock and the 24-hour clock.
EXTRA PRACTICE
INDEPENDENT ACTIVITY
▶ Writing Elapsed Time 15–30 Min
Number Stories(Math Masters, p. 180)
Students write a number story using fractions to represent elapsed time. Ask students to exchange and solve each other’s problems and then share their solution strategies.
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