Converting Measurements Using Ratios Day 2

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Objective

SWBAT: • Use ratios to convert measurement units using multiplication or division. • Convert measurements between the customary and metric system. • Apply knowledge of measurement conversions to solve word problems.

Big Idea

Which building is the world’s tallest building? Students use ratios to convert measurements between customary and metric systems. Students apply this knowledge to word problems.

Do Now

3 minutes

See my Do Now in my Strategy folder that explains my beginning of class routines.

Often, I create do nows that have problems that connect to the task that students will be working on that day.  Today I want students to quickly review the measurement facts that they are expected to know on our state test.   We check the answers together.  I stress to students that they need focus on memorizing these facts. 

Conversion Review

5 minutes

I tell students to get out their foldables from the previous lesson.  They can use it as a resource to complete the conversions.  As students work, I walk around to monitor student progress.  I am looking to see that students are using the correct measurement fact as well as setting up and labeling their ratios.  Students are engaging in MP5: Use appropriate tools strategically.

 We come back together and I ask students to share out their strategies and answers to problem 4.  I want students to realize that 7,000 pounds is equal to 3 ½ tons.

Comparing Measurements

5 minutes

I have a volunteer read the information and the question.  Students participate in a Think Pair Share.  Students are engaging in MP2: Reason abstractly and quantitatively and MP3: Construct viable arguments and critique the reasoning of others.   I call on students to share their thinking.   I ask students how that fact can help us determine whether Kate or Alexa is taller.  I want students to realize that if 1 inch is equivalent to 2.54 centimeters, we can use that fact to convert other amounts.  We set up the ratios together and determine which girl is taller.

Practice

10 minutes

Students work in partners on the problems.  I walk around and monitor student progress.  My goal is that the students complete problem 1.  If they complete problem 1 successfully, they will move on to problem 2.  A common mistake is to incorrectly set up or label the ratios.  I do not teach students to multiply when changing a “smaller” unit to a “larger” unit, or vice versa.  I believe that this short cut does not help students; rather it is one more procedure that they are likely to mix up or forget.  By using ratios, I believe students are able to understand that converting measurements is just creating equivalent ratios.

If students are struggling, I may ask one or more of the following questions:

  • What units are involved in the problem?
  • What are you trying to find?
  • How can you use the information to create ratios?
  • What operation are you going to use to create equivalent ratios?

With a few minutes left, I call on students to share their thinking to problem 1.  I call on students to share if they agree or disagree and why.  Students are engaging in MP3: Construct viable arguments and critique the reasoning of others.

 

Dr. Evil and Mini-Me

20 minutes

We watch the first video clip.  http://robertkaplinsky.com/work/mini-me/#prettyPhoto  I ask students, “What is the ratio, in inches, of Mini-Me’s height to Dr. Evil’s height?”  I explain to students that they will be working with their partner on this task.  There is information on this page and the next page that will help you.   I remind students that they can look back at their practice problems to get ideas.

As students work, I walk around and monitor student progress and behavior.  Students are engaging in MP1: Make sense of problems and persevere in solving them and MP2: Reason abstractly and quantitatively. 

If students struggle, I may ask one of the following questions:

  • What are you trying to figure out?
  • What do you know?
  • What extra information do you need?
  • How does this problem relate to the practice problems we did?  How is it different?

If students successfully answer the question, I may ask one of the following questions:

  • How did you find your ratio?
  • What does your ratio actually mean?
  • Challenge Questions

We come back together for the last 5 minutes.  Students share out their ratios and how they got them.  Then we watch the second video clip.  I ask students, “Why is your ratio different?  Which ratio is more reasonable?”  Students are engaging in MP2: Reason abstractly and quantitatively.   I want students to realize that if the ratio of Mini-Me to Dr. Evil was really 1/8, then for every 1 inch of Mini-Me’s height, Dr. Evil would have 8 inches of height.  Just by looking, we can see that Dr. Evil isn’t 8 times taller than Mini-Me.

Closure and Ticket to Go

7 minutes

I ask students why they would need to convert units from one system to another.  I pass out the Ticket to Go and the HW Converting Measurements Using Ratios Day 2.