Finding Common Denominators
Subject: Math
Grade Level: 4-5 (ages 9-11)
Time: 50 minutes
Lesson Objective:
Students will work with visual models to explore the relationship between equivalent fractions
and common denominators, and then apply their conceptual understanding to help them solve
problems involving the addition and subtraction of fractions with unlike denominators.
Common Core State Standards for Mathematics1:
ƒ
ƒ
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Use equivalent fractions as a strategy to add and subtract fractions.
Build fractions from unit fractions by applying and extending previous understandings of
operations on whole numbers.
Represent and solve problems involving addition and subtraction.
Overview:
Students often struggle with the algorithms used to solve problems involving fractions with
unlike denominators because they lack the conceptual foundation necessary for understanding
the steps required. In this Kidspiration® activity, students will work with Kidspiration Fraction
TilesΠto visually explore the relationship between equivalent fractions and common
denominators. They will use manipulatives, numbers and symbols to solve problems and show
their thinking.
Preparation:
This lesson requires the Kidspiration software application published by Inspiration Software, Inc.
30-day trials can be downloaded at <http://www.inspiration.com/kidspiration>.
Lesson:
1. Open Finding Common Denominators.kia from Kidspiration Starter>Activities>Math
and explain to students that they will use fraction tiles to solve addition problems.
© 2011 Inspiration Software, Inc. You may use and modify this lesson plan for any non-commercial, instructional use.
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Finding Common Denominators
2. The first page of the activity is an example. Read the directions aloud and talk about how
the tiles were used to find a common denominator. It may be helpful to walk through the
example from the beginning. If so, the first page of the activity can be unlocked ahead of
time. Delete the tiles and the answers in the green boxes and follow the directions as a
class to solve the problem. Try different tiles to show incorrect common denominators.
For example, with eighths, students will see that
number of eighths that is equivalent to
1
4
is equivalent to , but there is no
2
8
2
.
5
Solicit other ideas and continue trying different tiles until students see that 10 is the least
common denominator.
© 2011 Inspiration Software, Inc. You may use and modify this lesson plan for any non-commercial, instructional use.
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Finding Common Denominators
3. Instruct students to work independently to solve the five problems on pages 2-5 of the
activity. Students can use the Go to Next Page and Go to Previous Page buttons to
navigate through the pages. Circulate while students are working, asking them to
describe their thinking and ensuring that they are finding least common denominators.
4. If there is time remaining after students finish the five problems, have them add a page
to create and solve their own problem involving fractions with unlike denominators.
5. When students have finished the activity, come together as a class and go over each
problem. Some students may have solved problems by finding common denominators,
but not necessarily least common denominators. Discuss and show with tiles how
common denominators will always yield a correct answer, but not in simplest form. Use
the time to challenge common errors in adding fractions, such as adding the numerators
and denominators together. For example, show with fraction tiles that
equal
1
1
+
does not
4
2
2
.
6
© 2011 Inspiration Software, Inc. You may use and modify this lesson plan for any non-commercial, instructional use.
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Finding Common Denominators
Assessment:
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contributions to class discussions.
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Completed activities can be assessed for completion and correctness, paying careful
attention to students who found common denominators rather than least common
denominators. See Common Denominators Exemplar.kid for a sample completed
activity.
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Individual students can present their solutions to the eight problems included in the
activity. Presenters can be assessed on their models, solutions and the description of
their process to the class.
Adaptations / Extensions:
ƒ The activity can be modified to work on finding sums greater than one-whole by simply
aligning multiple whole trays horizontally and resizing the manipulatives on the
workspace as necessary.
ƒ
For those students who are ready, modify the activity to include more advanced work
with fractions²for example, sums of three or more fractions, such as
2
1
1
+
+ .
3
4
2
1
© Copyright 2011. National Governors Association Center for Best Practices and Council of Chief State
School Officers. All rights reserved. Learn more online at <http://www.corestandards.org>.
© 2011 Inspiration Software, Inc. You may use and modify this lesson plan for any non-commercial, instructional use.
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