Creating Word Problems for Multiplying Fractions

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SWBAT write an original word problem for multiplying fractions.

Big Idea

There's more to multiplying fractions than brownies.

Do Now

10 minutes

In the previous lesson my students worked on creating an area model for multiplying fractions, using this visual to develop an algorithm for multiplying fractions.  Today's Do Now is an informal assessment of my student's understanding of yesterday's work.

Do Now

Use a visual model to represent each problem, then use an algorithm to verify your answer.

  1.      3/4 of 7/8
  2.      2/7 of 1/3
  3.      9/10 of 1/6
  4.      2/5 of 2/3

After my students complete the Do Now, they will share their work with their group. I expect that students will have similar visual models, but if they differ, I will encourage students discuss their steps and determine why they have different answers. (MP3)

As students work, I will circulate throughout the groups to assess their understanding of multiplying fractions.  Students may have difficulty shading the area models, so I will be specifically looking for this.

Class Discussion

10 minutes

In yesterday's lesson we used the sharing of brownies as the anchor context for area models. Students also watched a video showing how to use KitKat bars to represent multiplying fractions. Building on these contexts, I will now engage students in a discussion of what multiplying fractions word problems might look like.  After reminding students of yesterday's work, I'll begin with this prompt:

What are other situations where area models would be used for multiplying fractions? 

This conversation is an important first step towards completing the next activity, when students will be asked to write word problems that involve multiplying fractions. Since the two examples they've seen focus on food, I expect students may offer suggestions such as a pack of gum, hershey bar, etc.  I will encourage them to think of other, non-food related, examples and continue the conversation until students seem excited about the number of ways that they can use multiplication of fractions. 

Group Work

20 minutes

After our discussion, I will ask students to work in groups on the assignment of writing an original word problem that can be solved by multiplying fractions.  I will state that students "must work together to write and solve the word problem."  I will suggest to students that they spend a few minutes brainstorming, before they choose a main idea to use as the context for a word problem.  

Students will have 20 minutes to write and solve the word problem.  The final problem and solution should be written on a sheet of paper and handed in to me.

Lesson Review

5 minutes

Before they leave class today, atudents will complete an Exit Ticket.  I will post the below word problems on the board for students to solve on an index card.  Students will have 5 minutes to complete the problems before handing it in to me.

1.  Yesterday, Peter's Snack Shack went through 1/3 of a bottle of ketchup. If they used 2/5 as much mustard as ketchup, how many bottles of mustard did they go through?

2.  Professor Dave weighed two pieces of metal for an experiment. The piece of iron weighed 5/6 of a pound and the piece of aluminum weighed 1/3 of a pound. How much more did the piece of iron weigh than the piece of aluminum?

The purpose of today's exit card is to assess whether students are able to identify what a word problem is asking of them.  I will use these cards to determine whether I need to spend more time on solving word problems.