Fraction Subtraction Showdown: Mastering Unlike Denominators!

Mathematics Grades 7th Grade 3:36 Video
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Lesson Description

Learn how to subtract fractions with different denominators by finding common denominators. Visualize fractions and understand the 'why' behind the math!

Video Resource

Subtracting fractions with unlike denominators introduction

Khan Academy

Duration: 3:36
Watch on YouTube

Key Concepts

  • Fractions
  • Unlike Denominators
  • Common Denominators
  • Equivalent Fractions
  • Least Common Multiple

Learning Objectives

  • Students will be able to identify fractions with unlike denominators.
  • Students will be able to find the least common denominator (LCD) of two or more fractions.
  • Students will be able to convert fractions to equivalent fractions with a common denominator.
  • Students will be able to subtract fractions with unlike denominators.

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing what a fraction represents (part of a whole). Briefly discuss what a denominator and a numerator are. Pose the problem: 'Imagine you have half a pizza, and your friend eats a third of the *whole* pizza. How much pizza do you have left?' Introduce the video from Khan Academy as a visual aid to solve this problem.
  • Video Viewing (7 mins)
    Play the Khan Academy video 'Subtracting fractions with unlike denominators introduction'. Instruct students to pay attention to how the fractions are visualized and how the common denominator is found.
  • Guided Practice (10 mins)
    Work through 2-3 example problems similar to the one in the video on the whiteboard. Involve students by asking them to suggest common denominators and the numbers to multiply by. Visualize the fractions using drawings (circles, rectangles) as demonstrated in the video.
  • Independent Practice (10 mins)
    Provide students with a worksheet containing 3-5 fraction subtraction problems with unlike denominators. Circulate to provide assistance and answer questions.
  • Wrap-up (3 mins)
    Review the key steps for subtracting fractions with unlike denominators. Emphasize the importance of finding the least common denominator to simplify calculations. Briefly discuss real-world applications of subtracting fractions.

Interactive Exercises

  • Fraction Visualization
    Use online fraction tools (e.g., visualfractions.com) to allow students to manipulate fractions and visually subtract them.
  • Real-World Problem Solving
    Present word problems that require students to subtract fractions with unlike denominators in a real-world context, such as measuring ingredients for a recipe or calculating remaining distance on a trip.

Discussion Questions

  • Why is it important to have a common denominator when subtracting fractions?
  • How does finding the least common denominator help you when subtracting fractions?
  • Can you think of a real-world situation where you might need to subtract fractions with unlike denominators?

Skills Developed

  • Problem Solving
  • Critical Thinking
  • Visual Representation
  • Fraction Manipulation

Multiple Choice Questions

Question 1:

What is the first step in subtracting fractions with unlike denominators?

Correct Answer: Find a common denominator

Question 2:

What is the least common denominator (LCD) of 1/4 and 1/6?

Correct Answer: 12

Question 3:

1/2 - 1/4 = ?

Correct Answer: 1/4

Question 4:

What is an equivalent fraction to 1/3 with a denominator of 6?

Correct Answer: 2/6

Question 5:

Why do we need to find a common denominator?

Correct Answer: To subtract the numerators easily

Question 6:

What is 2/3 - 1/6?

Correct Answer: 1/2

Question 7:

If you have 3/4 of a pizza and eat 1/8 of the *whole* pizza, how much pizza is left?

Correct Answer: 5/8

Question 8:

Which fraction is equivalent to 3/6?

Correct Answer: 1/2

Question 9:

To convert 1/5 to an equivalent fraction with a denominator of 10, what do you multiply both the numerator and denominator by?

Correct Answer: 2

Question 10:

What is 5/6 - 1/3?

Correct Answer: 2/3

Fill in the Blank Questions

Question 1:

Fractions with different denominators are called ________ denominators.

Correct Answer: unlike

Question 2:

The smallest multiple that two numbers share is called the least ________ ________.

Correct Answer: common multiple

Question 3:

When subtracting fractions, you only subtract the ________, not the denominator.

Correct Answer: numerators

Question 4:

A fraction that represents the same amount as another fraction is called an ________ fraction.

Correct Answer: equivalent

Question 5:

To get a common denominator for 1/2 and 1/5, you could use ________ as the common denominator.

Correct Answer: 10

Question 6:

Before subtracting fractions, make sure the denominators are the ________.

Correct Answer: same

Question 7:

The top number in a fraction is called the ________.

Correct Answer: numerator

Question 8:

The bottom number in a fraction is called the ________.

Correct Answer: denominator

Question 9:

1/4 is equivalent to ________/8.

Correct Answer: 2

Question 10:

To subtract 1/3 from 1/2, you need to rewrite them with the common denominator of ________.

Correct Answer: 6

Educational Standards

7.N.1:Read, write, represent, and compare rational numbers, expressed as integers, fractions, and decimals. Explain and apply the concept of absolute value. 7.N.1.2:Recognize and generate equivalent representations of rational numbers, including equivalent fractions. 7.N.2.5:Model and solve problems using rational numbers involving addition, subtraction, multiplication, division, and positive integer exponents.

Teaching Materials

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