In this lesson, students solve problems about percent error, a way to describe error as a percentage of the actual amount. First, students consider measurement error, which is the positive difference between a measured amount and the actual amount. Students see how measurement error can arise in two different ways: from the level of precision in the measurement device and from human error. They learn the convention of expressing measurement error as a percentage of the correct value. 

Next, students interpret situations and identify which value is the correct amount that the error should be compared to. They make sense of problems as they solve for the erroneous value, the correct value, or the percentage (MP1). As students relate situations involving percent error to previous work they have done with percent increase or decrease, they are making use of structure (MP7).

In an optional activity, students consider error tolerance expressed as a maximum acceptable percent error to determine values that fall within or outside of the range.