Adding and Subtracting Fractions: Find the Common Denominator

SubstitutePlans.com
Mathematics · Math 6-7
SP-MATH68-001 · Free to print and use in your classroom · substituteplans.com
Page 2
Adding and Subtracting Fractions: Find the
Common Denominator
Mathematics · Math 6-7 · Grades 6-7 · 50 minutes
Time needed
50 minutes (one class period)
Prep
Copy the 2-page worksheet (one per student). Write the worked example on the board.
Technology
None. Calculators are not needed.
Student
independence
High. Students work alone, then compare with a partner.
Copies to make
One 2-page worksheet per student
Materials
Pencils, Worksheet, Whiteboard or chalkboard
Goal for today: Students will add and subtract fractions and mixed numbers with unlike denominators by rewriting
them with a common denominator, and will identify errors in sample work.
Before the bell
☐ Copy the worksheet, one per student (2 pages).
☐ Write on the board: 1/2 + 1/3 → 3/6 + 2/6 = 5/6. Under it write: “Step 1: same denominator. Step 2: add or
subtract the tops only. Step 3: simplify.”
☐ Keep the answer key on your desk. You do not need to solve anything yourself.
Say this to start
Good morning! Your teacher left a fraction practice for today. You will add and subtract fractions, then play detective
and find mistakes in other students’ work. The steps are on the board and everything else is on the worksheet. I will
walk around, but you are in charge of checking your own work.

SubstitutePlans.com
Mathematics · Math 6-7
SP-MATH68-001 · Free to print and use in your classroom · substituteplans.com
Page 3
Run of show
Minutes
What you do
What students do
0–5
Take attendance the way the school requires. Hand out the
worksheet face down and ask students to wait.
Settle in, take out a pencil, and wait for
directions.
5–12
Read the example on the board aloud, slowly: 1/2 + 1/3.
The bottoms are different, so rewrite both as sixths: 3/6 +
2/6 = 5/6. Add only the tops. The bottom stays 6.
Follow along. Copy the example in the
margin if they like.
12–30
Tell students to complete questions 1–6 in the work boxes.
Walk the room. If a student is stuck, ask, “What number
can both bottoms go into?”
Solve each problem on their own and show
the common denominator.
30–38
Tell students to finish the Error Detective table, then
questions 7–10. Partners may compare answers quietly.
Decide which sample solutions are right, fix
the wrong ones, and answer the word
problems.
38–45
Read the answers for questions 1–6 aloud from the key.
Students mark each one right or wrong. They do not need
to turn in a corrected copy.
Check their work and fix mistakes in a
different color if possible.
45–50
Remind students to finish question 10 (the last line). Then
collect all worksheets.
Write one sentence for question 10. Hand
in the worksheet.
If things go wrong
• If students say, “We have not learned this,” tell them it is practice and the example on the board shows every
step. Pair them with a neighbor who is comfortable.
• If a student does not know how to find a common denominator, tell them to list multiples of each bottom
number until one number appears on both lists (for 4 and 6: 4, 8, 12 and 6, 12).
• If a student finishes in under 20 minutes, check that every problem shows the new denominator, then use the
early finisher list.
• If the class is noisy, remind them it is individual practice time. Partners may whisper only during the Error
Detective table.
Early finishers
• Make up two fraction addition problems with different denominators. Solve them on the back and trade with a
neighbor.
• Write a short word problem that matches 3/4 − 1/3 and solve it.
Support and challenge
• Support: Let students draw a rectangle or a fraction bar for each problem. Ask them to complete only
questions 1, 2, 3 and 7.
• Challenge: Ask students to find 1/2 + 1/3 + 1/4 and show the common denominator they chose.

SubstitutePlans.com
Mathematics · Math 6-7
SP-MATH68-001 · Free to print and use in your classroom · substituteplans.com
Page 4
Notes for the teacher (you fill this in)
Jot a few lines before you leave. A full Daily Sub Report is in the free Sub Survival Kit at SubstitutePlans.com.
How far the class got / what to pick up next:
Students who were especially helpful:
Anything the teacher should know: