Grocery Store Problem Solving

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SWBAT solve real world problems involving pounds and ounces.

Big Idea

In order to further develop students' understanding of measurement units, it is important to provide students with opportunities to solve problems involving measurement.


10 minutes

For today's lesson, I wanted to give students as much time as possible to solve word problems involving pounds and ounces so spent a little time as possible introducing the lesson: Fourth graders, today's goal is: I can solve real world problems involving pounds and ounces. As I wrote the goal on the board, students also wrote it on a new page in their math journals. 

I explained: Today, you get to go shopping! Each pair of students will be given a grocery store flyer. In order to solve each word problem today, you'll have to look in the flyer for more information. I passed out a Grocery Store Flyer* to every two students. I already have students' desks carefully arranged in groups of 4-5, based upon skills, behavior, leadership qualities, communication skills, and processing skills. This makes assigning partners quite easy as I can quickly pair up students within each group to save time. Students were instantly motivated to use this real-life application. I was also excited, knowing that this lesson would help students understand how math is connected to the real world (Math Practice 4: Model with Mathematics). 

*The night before this lesson, I went to a grocery store and asked for a handful of flyers. I could have also just taken pictures of products, arranged the pictures in a word document, and distributed a simpler version: Smith's Flyer.



Teacher Demonstration

20 minutes

After passing out the flyers, I brought my kids back together: Classss!!!! Students responded, "Yessssss!" I want to solve one problem together and then, you'll use a grocery store flyer to solve the rest of the problems on your own or with your partner. I'll be passing out a list of word problems. Please cut out each problem. Then, go ahead and paste the first problem at the top of the page in your journal. I modeled this using a student's journal and then passed out the Grocery Store Problems

As soon as students finished cutting the problems out and pasting the first problem in their math journals, I read the first problem aloud a couple of times to make sure all students heard: If you purchase three pounds of Kroger butter, how much will it cost? What information is missing? Students responded "The cost of the butter!" Immediately, students began searching for the butter in the flyer and before long many students were excitedly saying, "I found it!" "It's $1.99!" I read the problem aloud once more. Students then said, "We need to know how much it weighs!" "16 ounces!" "That's one pound!" So what do we need to do to solve this problem? "Add more butter until you get to three pounds!" I demonstrated how to demonstrate their thinking on the board: First Problem while asking guiding questions: Okay, so if I had 1 butter, it equals 16 ounces, which also equals 1 pound. What if I had two packages of butter? How many pounds do we have now? What do we need to do next? Students followed along, and completed the first problem in their journals. 

After solving the first problem, students anxiously asked, "Can we go on to the next problem?!" 


Student Practice

70 minutes

At this point, I went over problem solving expectations: 1. You can work on your own or with your partner. 2. Please use a half page to solve each problem. 3. Make sure to show your thinking. 4. For each problem, write "Answer" and provide a labeled answer. Students jumped right in and began solving problem #2. 

During this independent work time, I conferenced with every student. I looked for misconceptions and opportunities to push student thinking. Whenever I discovered an incorrect answer on a student's paper, I took the time to ask guiding questions. At times, I only had to ask the student to reread the problem. Other times, I asked a string of questions to lead the student to a solid understanding of the problem. Either way, the goal is for the student to have the tools necessary to solve the next problem independently. 

Just after we began working, a student pulled me over to her desk and showed me how she rounded up to solve the first problem and then compensated by subtracting three cents at the end: Problem #1. I was so proud of her for showing her work using a strategy besides the modeled problem solving method.

Here, a student explains his thinking on Problem #2. I liked how he checked his answer using multiplication. This video also demonstrates how eager the students were to solve as many problems as possible. He could hardly stand having to slow down to show his work! 

This student, Problem #3, simply needed help with organizing his thoughts so I drew an In & Out box on his paper to get him going. From there, he was ready to go and doubling numbers in his head. I continually brought the student back to the wording in the question. Meanwhile, a nearby student, listening in on our conversation realized that she couldn't just buy 2 oz. of raspberries when they are sold in 6 oz. containers! 

On Problem #4, many students wanted to know how many apples were in a pound. At times, I would take the students over to our classroom scale to help them realize that they were finding the cost per pound, not per apple! 

Here, Problem #5, I worked with a student to represent his thinking on paper. He likes to complete math in his head without explaining. I have to say that this student has struggled with math this year because he has a hard time paying attention and listening to directions. He often misses key concepts. To help support him this year, I will often reteach concepts and/or encourage peer conversations. This was the first lesson this year that he was 100% on task and motivated to learn. I kept hearing him say, "This is fun!" It was great to see him starting to catch on. 

Finally, about five students got to Problem #6. This student had gotten the correct answer by repeatedly adding 50. While she got the correct answer, I wanted to challenge her to verify her answer using another strategy, the In & Out box. She began using a doubling strategy and then I asked her if she could add two numbers to get a friendly number. She recognized 2 bags + 8 bags = 10 bags, but had difficulty figuring out the number of pounds. I modeled how to add two quantities together on a simpler In & Out box. She then understood the strategy and applied it to her own In & Out box! 



2 minutes

Today, students worked all the way to the end of our math period, solving these math problems. Early finishers checked and revised their work with other students. Most students were able to solve problems one through five. After solving the first few problems, which were easier, students really built up a momentum! They didn't want our math time to end! I did take a couple minutes to celebrate students who persevered, verified answers, and took the time to make sure their work was precise.