Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Lesson 2 Finding a Fraction of a Fraction Problem Solving: Measuring With a Metric Ruler Finding a Fraction of a Fraction How do we use fraction bars to find a fraction of a fraction? In the last lesson, we looked at the multiplication of whole numbers by 1 fractions. When we multiply 1 2 · 2, we find 2 of 2. 2 When we multiply 2 3 · 3, we find 3 of 3. Now let’s multiply a fraction by another fraction. 4 1 4 When we multiply 1 2 · 5, we find 2 of 5 . Let’s complete this problem using fraction bars. 1 4 2·5 This fraction bar shows 4 5. Now we focus on just the shaded part and we take half of this. 1 There are four total shaded parts. If we take 2 of the shaded parts, we have 2 parts. We know that the 2 parts are fifths, so the answer to the problem is 1 4 2 2·5=5 The answer is smaller than the starting number, 4 5 . It’s smaller because 4 4 we are only finding a part of the fraction 5 . We are taking 1 2 of 5 . 90 Unit 2 • Lesson 2 Lesson 2 Using fraction bars helps us see what it means to multiply fractions. Let’s use fraction bars to solve another problem. Example 1 Find 15 · 5 8 using fraction bars. 1 5 5·8 5 We can think of this as 1 5 of 8 . First, we draw the fraction bar for 5 8 . This fraction bar has 8 total parts and 5 shaded parts. Let's focus on the shaded part. We can find 1 5 of it because there are 5 1 parts shaded and 5 is 1 part. 1 There are 5 total shaded parts. If we take 5 of the shaded parts, we have 1 part. Each part is an eighth, so the answer to the problem is 1 8. 1 Again, the answer is smaller than both 5 8 and 5 . We are finding a 1 5 fractional part of 5 8 . We are finding 5 of 8 . Apply Skills Turn to Interactive Text, page 50. When we multiply using fractions, we are taking a portion of another fraction, and that is why the answer or product is often a smaller number. Reinforce Understanding Use the mBook Study Guide to review lesson concepts. Unit 2 • Lesson 2 91 Lesson 2 Problem Solving: Measuring With a Metric Ruler Vocabulary How do we use a metric ruler? metric ruler millimeters centimeters When we measure small objects with a metric ruler , we use units called millimeters and centimeters . Here is an example of a metric ruler that shows these units. The metric ruler looks like this: cm 1 2 3 4 5 6 7 8 9 10 11 The smallest units on the metric ruler are millimeters. cm 1 3 Ten millimeters make up 1 centimeter. On a metric ruler, the centimeters are numbered. There are 5 millimeters in 1 2 centimeter. cm 1 Problem-Solving Activity Turn to Interactive Text, page 51. 92 Unit 2 • Lesson 2 3 Reinforce Understanding Use the mBook Study Guide to review lesson concepts. 12 Lesson 2 Homework Activity 1 Use the fraction bar to help you solve the problems. 1. 1 2 · 46 2 6 1 3 1 2. 3 · 6 6 1 2 1 2 3. 2 · 6 6 Activity 2 Use the fraction bar to help you solve the problems. 1. 1 2 · 24 1 4 1 3 1 2. 3 · 4 4 3. 2 · 4 4 Activity 3 Draw the points, line segments, rays, and lines. Follow the instructions for labeling. 1. Draw a ray. Label it AB. 2. Draw a line segment. Label it CD. 3. Draw a point. Label it X. 4. Draw a line. Label it EF. 5. Draw a line segment. Label it MN. Activity 4 • Distributed Practice Solve. 1. 253 + 28 281 2. 125 11 114 3. 173 88 85 4. 17 3 51 Copyright 2010 by Cambium Learning Sopris West®. All rights reserved. Permission is granted to reproduce this page for student use. Unit 2 • Lesson 2 93