The activities in this optional lesson challenge each student to determine their exact age, how many times their heart has beaten, and how many hairs are on their head. In each, students must decide how precise to be in their response. Determining their age allows more certainty than the other calculations.

This lesson is made of activities sometimes called “Fermi problems” after the famous physicist Enrico Fermi. A Fermi problem requires students to make a rough estimate for quantities that are difficult or impossible to measure directly. Often, they use rates and require several calculations with fractions and decimals, making them well-aligned to grade 7 work. Fermi problems are examples of mathematical modeling (MP4) because one must make simplifying assumptions, estimates, research, and decisions about which quantities are important and what mathematics to use. They also encourage students to attend to precision (MP6) because one must think carefully about how to appropriately report estimates and choose words carefully to describe the quantities. This lesson relies on skills developed in Unit 2 and Unit 5.

Any of these tasks can stand on its own. Teachers should select those that they have time for. Doing all three activities would likely take more than a single class period. Teachers should leave plenty of time for discussion, including why the quantities in question are difficult to measure and how precise the estimates should be.