Lesson Plan
Fraction Subtraction Fun!
Students will be able to subtract fractions with like denominators by using visual models and solving basic problems.
Understanding how to subtract fractions helps us share and divide things fairly, like slices of pizza or parts of a cake. It's a key step in becoming a math whiz!
Audience
2nd Grade Students
Time
30 minutes
Approach
Visual modeling and guided practice.
Materials
- Warm-Up: Subtracting Shapes!, - Fraction Subtraction Slides, - Fraction Fun Activity, - Whiteboards or scratch paper, and - Markers or pencils
Prep
Prepare Materials
10 minutes
Review all generated materials: Warm-Up: Subtracting Shapes!, Fraction Subtraction Slides, and Fraction Fun Activity. Gather whiteboards/scratch paper and markers/pencils for students.
Step 1
Warm-Up: Subtracting Shapes!
5 minutes
Begin with the Warm-Up: Subtracting Shapes! activity. Have students draw a shape, divide it into equal parts, shade some parts, and then erase a few shaded parts to represent subtraction. Discuss their findings as a class.
Step 2
Introduction to Fraction Subtraction
10 minutes
Use the Fraction Subtraction Slides to introduce the concept of subtracting fractions with like denominators. Focus on visual examples and concrete representations. Explain that when denominators are the same, we only subtract the numerators.
Step 3
Guided Practice
10 minutes
Work through a few examples together using the slides and whiteboards. Model how to draw the fractions and then subtract by 'erasing' parts. Emphasize keeping the denominator the same.
Step 4
Independent Practice: Fraction Fun Activity
5 minutes
Distribute the Fraction Fun Activity worksheet. Students will complete the activity, drawing models for each problem. Circulate to provide support and clarification.
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Slide Deck
Fraction Subtraction Fun!
Get ready to make fractions disappear!
Welcome students and get them excited for a fun math lesson!
What's a Fraction Again?
Remember, a fraction tells us about parts of a whole!
- Numerator: How many parts we have.
- Denominator: How many total parts make up the whole.
Quickly review what a fraction is: a part of a whole. Use examples like pizza or cake.
Subtracting Fractions!
Imagine you have a pizza with 8 slices.
You eat 3 slices. How many slices are left?
That's subtracting fractions!
Introduce the idea of taking away parts of a whole when the whole is divided equally. Use a visual to explain.
The Big Rule!
When we subtract fractions and the bottom numbers (denominators) are the same, we only subtract the top numbers (numerators)!
The denominator stays the same because the size of the pieces doesn't change!
Explain the key rule: only subtract the top numbers (numerators) when the bottom numbers (denominators) are the same.
Let's Try One! Example 1
You have a chocolate bar with 6 equal pieces. You eat 2 pieces.
How much of the chocolate bar is left?
$\frac{5}{6} - \frac{2}{6} = ?$
Think: 5 - 2 = ?
So, $\frac{3}{6}$ of the chocolate bar is left!
Walk through the first example step-by-step. Encourage students to draw along on their whiteboards.
Your Turn! Example 2
Sarah had $\frac{7}{8}$ of a pie. Her friend ate $\frac{3}{8}$ of the pie.
How much pie is left?
$\frac{7}{8} - \frac{3}{8} = ?$
Think: 7 - 3 = ?
So, $\frac{4}{8}$ of the pie is left!
Present a second example for students to try independently or with a partner before revealing the answer.
Remember the Rule!
When the denominators are the same, subtract the numerators!
Keep the denominator the same!
Now, let's practice with our Fraction Fun Activity!
Summarize the lesson and transition to the activity.
Warm Up
Warm-Up: Subtracting Shapes!
Objective: Visualize subtracting parts of a whole.
Instructions:
-
Draw a Shape: On your whiteboard or scratch paper, draw one of these shapes: a circle, a square, or a rectangle.
-
Divide it Up: Divide your shape into 4, 6, or 8 equal parts.
-
Shade Some: Shade in a certain number of those parts (make sure to leave at least one unshaded part).
- What fraction represents the shaded parts?
-
Subtract Some: Now, imagine you are subtracting some of those shaded parts. Lightly cross out or "erase" 1 or 2 of your shaded parts.
- What fraction represents the parts you "subtracted"?
-
Write the Problem: Write down the subtraction problem you just created and solve it! For example, if you shaded 3 out of 4 and crossed out 1, you would write $\frac{3}{4} - \frac{1}{4} = \frac{2}{4}$.
Share your work with a partner or the class!
Activity
Fraction Fun Activity: Subtracting with Pictures!
Instructions: For each problem, draw a picture to show the fractions and then subtract. Write your answer as a fraction.
Problem 1
You have a pizza cut into 6 equal slices. You started with $\frac{5}{6}$ of the pizza. You ate $\frac{2}{6}$ of the pizza.
Draw it!
What fraction of the pizza is left?
Problem 2
Sarah had a chocolate bar broken into 4 equal pieces. She had $\frac{3}{4}$ of the chocolate bar. She gave her friend $\frac{1}{4}$ of the chocolate bar.
Draw it!
What fraction of the chocolate bar is left?
Problem 3
The baker made a big cake and cut it into 8 equal pieces. There was $\frac{7}{8}$ of the cake left. A customer bought $\frac{3}{8}$ of the cake.
Draw it!
What fraction of the cake is left?
Answer Key
Fraction Fun Activity Answer Key
Problem 1
You have a pizza cut into 6 equal slices. You started with $\frac{5}{6}$ of the pizza. You ate $\frac{2}{6}$ of the pizza.
Thought Process:
- Understand the initial amount: The problem states you started with $\frac{5}{6}$ of the pizza. This means the pizza was divided into 6 equal parts, and you had 5 of those parts. Visualizing this would involve drawing a circle divided into 6 sections and shading 5 of them.
- Understand the amount subtracted: You ate $\frac{2}{6}$ of the pizza. This means 2 of those 6 slices were removed.
- Perform the subtraction: Since the denominators are the same (6), we only subtract the numerators: $5 - 2 = 3$.
- Formulate the answer: The denominator stays the same, so the answer is $\frac{3}{6}$.
Visual Representation:
_ _ _
/ _|_ \
| / | |
| / | |
\_ _|_/
(Imagine 5 sections shaded, then 2 of those crossed out)
Answer: $\frac{5}{6} - \frac{2}{6} = \frac{3}{6}$ of the pizza is left.
Problem 2
Sarah had a chocolate bar broken into 4 equal pieces. She had $\frac{3}{4}$ of the chocolate bar. She gave her friend $\frac{1}{4}$ of the chocolate bar.
Thought Process:
- Understand the initial amount: Sarah had $\frac{3}{4}$ of the chocolate bar. This means the bar was divided into 4 equal parts, and she had 3 of them. Visualizing this would involve drawing a rectangle divided into 4 sections and shading 3 of them.
- Understand the amount subtracted: She gave away $\frac{1}{4}$ of the chocolate bar. This means 1 of those 4 pieces was removed.
- Perform the subtraction: Since the denominators are the same (4), we only subtract the numerators: $3 - 1 = 2$.
- Formulate the answer: The denominator stays the same, so the answer is $\frac{2}{4}$.
Visual Representation:
_________
|###|###|# |
|###|###|# |
|###|###|# |
|___|___|_|
(Imagine 3 sections shaded, then 1 of those crossed out)
Answer: $\frac{3}{4} - \frac{1}{4} = \frac{2}{4}$ of the chocolate bar is left.
Problem 3
The baker made a big cake and cut it into 8 equal pieces. There was $\frac{7}{8}$ of the cake left. A customer bought $\frac{3}{8}$ of the cake.
Thought Process:
- Understand the initial amount: There was $\frac{7}{8}$ of the cake left. This means the cake was divided into 8 equal parts, and 7 of those parts remained. Visualizing this would involve drawing a circle divided into 8 sections and shading 7 of them.
- Understand the amount subtracted: A customer bought $\frac{3}{8}$ of the cake. This means 3 of those 8 pieces were removed.
- Perform the subtraction: Since the denominators are the same (8), we only subtract the numerators: $7 - 3 = 4$.
- Formulate the answer: The denominator stays the same, so the answer is $\frac{4}{8}$.
Visual Representation:
_ _
/ | \
/ | \
|----+----|
| \ | / |
\_ _|_ _/
\_/
(Imagine 7 sections shaded, then 3 of those crossed out)
Answer: $\frac{7}{8} - \frac{3}{8} = \frac{4}{8}$ of the cake is left.