Natural Packages

  • Natural Packages

    Grades: 6th to 8th
    Periods: 2
    Author: Mark Roddy


    • Per team: 1 electronic scale
    • Day 1: various food items in “natural packages” (e.g., bananas, apples, oranges, grapes, hard-boiled egg, etc. (see below)
    • Day 2: additional food items in human-made packages (e.g., raisins in boxes, canned peaches, cans of juice, etc.; see below)

    Note: Be sure to consider food allergies in your classroom as you plan this investigation. 

    Instructional Plan

    Natural Packages Tiny CoverNature packages things in peels and shells and other sorts of outer wrappings that we just throw away or compost. People package things in bags and boxes and cans and so forth. Which kinds of packages are the most efficient? Learners have fun with food as they develop a clear conceptual basis of understanding of percentages. Read the story behind Natural Packages here

    Day 1

    15 minutes: Introduce Investigation and Central Question

    Begin by asking students the following questions and recording their predictions.

    • Did anyone bring a lunch to school today?
    • Does anyone have a banana?
    • How do you eat a banana?
    • How much of the banana doesn't get eaten? How much is just “packaging”?

    Steer the discussion toward the idea of a percentage that will be used to define “packaging efficiency.” Example: If a whole banana weighs 120 grams and the peel weighs 30 grams, then the edible part must weigh 120 - 30 = 90 grams. The ratio of edible part to the whole thing, the packaging efficiency, is 90 : 120, or 90/120. A percentage is just a way of comparing one part of a whole to a standard of 100. It can be set up just that way: 90/120 = x/100. This is the key ratio. It may be read as “90 is to 120 as x is to 100.” Changing 90/120 to a decimal, we get 0.75 = x/100 and so x = 0.75 x 100 or 75 percent. The packaging efficiency of that banana was 75%. 


    It is important that they see the way the percent is connected to the ratio, so it may help to practice this a few times and to repeat the verbal formulation as you write the mathematical expression. For example, a banana that is more efficient in its packaging might have a weight of 140 grams for the whole thing and 110 grams for the edible part. Then you would say, “110 is to 140 as x is to 100.” You want them to see that the statement always ends with “as x is to 100.” That is the nature of the process. You are comparing a part of a whole to the corresponding part as if the whole were composed of 100 pieces. In this case 110/140 = 0.79 to the nearest one hundredth, and so its efficiency may be expressed as 79 percent-literally, 79 per 100; 110 per 140 is equivalent to 79 per 100, or 79%. 


    We can compute this ratio for anything that has a package and a useful part inside the package. Ask students what they would do to find the packaging efficiency for an orange. How about an apple? A bunch of grapes? (The packaging is the stems!) A carrot? (To peel or not to peel, that is the question.) How about a hard-boiled egg? A peanut in its shell seems straightforward but will present challenges as you discover that a single peanut shell is likely to be too light to be weighed on a normal electronic scale. These are all natural packages, and each will have a different efficiency. All will rely on this simple proportional relationship:

    Natural Packages Image 1

    The central question for this investigation is this:

    • How efficiently is this item packaged?

    20 minutes: Conduct Investigation and Gather Data

    Split the class into teams of two to four students. Each team will have a scale and a different food item (or items if you have time for multiple trials on each food). Make a chart on the board or consider using a Google Sheet™ to record and share data if students have networked laptop computers. Make sure students predict the packaging efficiency for their food before they conduct the investigation. See figure 1 for a sample data sheet for the class results.


    Natural Packages Image 2




    Note: If possible, conduct this investigation in concert with another class working on the same investigation. Your students can then trade information and results, thereby increasing their sample size. This connection increases motivation to get good results and to express these data in ways that will be understood by others. 


    15 minutes: Consider Results

    Take a look at the chart with its different efficiency percentages. As a way to review and solidify understanding, ask for a team or two to explain what they did in order to get their results. Consider the implications of the differences you are finding for the packaging efficiencies of the different food items.

    • Why, for example, does the banana have a larger percentage of its mass devoted to packaging than does a hard-boiled egg?
    • What is the function of the banana peel?
    • What is the function of the eggshell?
    • How are the environments in which a banana and an egg develop the same? How are they different?

    These questions may feel more like science than math, but this allows math to extend beyond the walls of the math classroom and into the realm of sense making.


    Finish this session by calculating an average efficiency percentage for all of these natural packages.


    5 minutes: Preview of Day 2

    This first day has been directed at natural packages, packages constructed by nature-but humans package food items too. Day 2 of the investigation is directed at a similar investigation, but this time directed at human packaging and at consideration of the ways in which natural and human-made packaging are similar and different. Ask students to think of some examples of human-made packages (e.g., peanuts in plastic jars or eggs in cartons). When we buy packaged food items at a grocery store, how efficiently are they packaged? Record some of their estimates.


    Invite students to bring an item they would like to investigate on day 2. Let them know that the food will probably not be edible when the investigation is done!


    Note: You should be prepared on day 2 to supply human-packaged food items for the class because some students may not bring items or may bring items that do not lend themselves easily to the investigation. 

    Day 2

    15 minutes: Introduce Human-Made Packages

    Collect the volunteered human-packaged food items at the front of the room, and supplement them with the items you brought. If there is one that corresponds to a food you investigated yesterday, start with that. For example, a plastic bag with dried banana chips recalls the banana. A box of raisins is the human-packaged equivalent of a bunch of grapes. Drinking a can or carton of orange juice is similar to eating an orange except that humans have intervened and repackaged the orange. Sort of. Investigate the packaging efficiency of one such item. With a jar of shelled peanuts, for example, you can weigh the whole thing, dump the peanuts into a bowl and weigh the jar, which is the packaging. Then, just as in day 1, you can calculate the packaging efficiency and see how it compares to the packaging efficiency of nature with the peanut and the peanut shell. This allows you to review the concept of the percentage as a ratio and the process for calculating percentages.


    Assign an item or items to each team and have them collect the materials they will need to investigate their item(s).


    15 minutes: Conduct Investigation and Gather Data


    As on day 1, you will make a chart on the board or in a shared spreadsheet so that students can record their results as they become available. You will have a chance to circulate around the classroom and assist teams as needed.


    15 minutes: Discuss and Generalize Results


    When all of the data have been collected, calculate a mean for the human-made packages just as you did for the natural packages. How do they compare? Is this a fair comparison if we are really interested in the efficiency of the packaging? What do we mean by “efficiency” in this case? Is there a difference between the “wasted” part of a natural product and that of a human-made product? What is the function of the packages people manufacture, and how do they differ from the function of packaging in nature? Which kinds of packages are more likely to be recycled? Why? These questions allow students to see mathematics as a sense-making endeavor rather than a set of exercises. 



    Assessments and Extensions

    Natural Packages Image 3Assessments (Be sure to show your work.)

    1. You order a cool thing through Amazon. A brown box is left on your doorstep. In the brown box is some packing material and a red box with the cool thing inside. When the brown box is empty, it weighs 140 grams. The red box weighs 80 grams when it is empty. The packing material weighs 20 grams. The cool thing weighs 450 grams. If the cool thing is the only part you really care about, what is the packaging efficiency for this process?
    2. Here are the packaging efficiencies for a sample of 5 walnuts. What is the mean packaging efficiency for these walnuts?
      Walnut 1: 45%, Walnut 2: 50%, Walnut 3: 55%, Walnut 4: 45%, Walnut 5: 60%.

    Mean packaging efficiency = ____________



    There are many ways to extend this investigation. Two examples follow.

    1. Buy a bunch of bananas and conduct the packaging efficiency investigation on a banana every other day until you deplete the bunch. Students will discover that as the remaining bananas ripen, their peels become thinner and the ratio of edible part to whole item changes. Of course, at some point the bananas become . . . less desirable . . . so that the edible part suddenly becomes zero.
    2. Human packaging of liquids presents a number of interesting investigations. Juice may be found in small cans, medium cans, and large cans. How does the packaging efficiency vary as the container gets larger? Juice can also be purchased in glass bottles, plastic bottles, and in cartons. How do these compare to one another for efficiency? 

    Questions and Reflections

    See questions embedded within the Instructional Plan.

    Objectives and Standards

    Learning Objectives

    • (Concept) Students will build their understanding of percentages.
    • (Skill) Students will develop their ability to compute percentages.
    • (Skill) Students will be able to calculate the mean of a simple data set.
    • (Disposition) Students will continue to develop a positive disposition regarding the use of mathematics to make sense of the world. 


    Common Core State Standards for Mathematical Content

    Grade 6

    • 6.RP.3.C Find a percent of a quantity as a rate per 100 (e.g., 30% of a quantity means 30/100 times the quantity); solve problems involving finding the whole, given a part and the percent.
    • 6.SP.2 Understand that a set of data collected to answer a statistical question has a distribution which can be described by its center, spread, and overall shape.

    Grade 7

    • 7.SP.2 Use data from a random sample to draw inferences about a population with an unknown characteristic of interest.

    Common Core State Standards for Mathematical Practice

    • SMP 2 Reason abstractly and quantitatively.
    • SMP 4 Model with mathematics.

    Related Resources

    Natural Packages