The goal of this activity is to build students’ intuition for 1 pound, 1 ounce, and the relationship between the two units. Students use labels on food packaging to reason about how pounds and ounces are related, and then use what they learn to convert pounds to ounces. Students reason abstractly and quantitatively when they determine the relationship between pounds and ounces from food labels (MP2).

Note that the quantities shown on food packaging or nutritional labels are often rounded rather than exact. For instance, a package labeled “32 ounces (2 pounds)” may contain 31.8 ounces but be labeled as 32 ounces or 2 pounds. In this activity, for the purposes of learning that one unit is 16 times the other, students will take the labels at face value. Consider explaining (during the Activity Synthesis) that, in reality, the label may not match the content exactly.

The blackline master includes images that can be used for the activity. If desired and if practical, actual packaged food could be used instead. In that case, be sure to choose items with whole numbers of pounds and ounces, and to exclude items that show that 1 pound is equivalent to 16 ounces, as students reasoning about the equivalence is the point of the activity. 

• Invite selected students to share their conclusions about the relationship between pounds and ounces. 
• Highlight explanations that make it clear that 1 pound is 16 times as much or as heavy as 1 ounce. 
• Display the table and invite students to share the amounts in ounces and their reasoning. 
• If needed, point out that the abbreviation “lb” is used for pounds and “oz” is used for ounces. 

In the first activity, students learned that one pound is 16 times as heavy as 1 ounce. Here they apply this knowledge to convert quantities into ounces and to solve multi-step problems. The quantities include a fractional number of pounds and one quantity expressed in a combination of pounds and ounces.

As in earlier lessons in which they encountered a fractional amount of a unit of measurement, students are not expected to find the number of ounces in pound by writing . Instead, they can reason about half of a quantity, using their understanding of fractions and by dividing an amount by 2. Those who do write represent the situation correctly, but this reasoning and the related operation will be developed in grade 5.

• Select students to share their responses and their reasoning. Record their responses for all to see.
• Clarify that sometimes both units are used to express a quantity that is not a whole number of pounds (as is the case with “2 pounds 8 ounces of pinto beans”).
• Select students who used different strategies to solve the last problem to share.