# Lesson 15

Error Intervals

### Lesson Narrative

This lesson is optional. In this lesson, students find and analyze intervals of possible error based on maximum possible errors.

This material gives students a solid foundation for future work in statistics. It is not necessary at this stage to emphasize the idea of a margin of error which defines a range of possible values. It is enough for students to see the values falling into that range, as preparation for future learning.

### Learning Goals

Teacher Facing

• Comprehend that manufacturers often define a maximum acceptable percent error for characteristics of their products.
• Determine what information is needed to solve a problem involving percent error. Ask questions to elicit that information.
• Generate values that fall within the acceptable range for a measurement, given a maximum percent error.

### Student Facing

Let’s solve more problems about percent error.

### Required Preparation

Print and cut cards from the Info Gap: Quality Control activity blackline master. One copy of the blackline master will be used for every 4 students.

### Student Facing

• I can find a range of possible values for a quantity if I know the maximum percent error and the correct value.

### Glossary Entries

• measurement error

Measurement error is the positive difference between a measured amount and the actual amount.

For example, Diego measures a line segment and gets 5.3 cm. The actual length of the segment is really 5.32 cm. The measurement error is 0.02 cm, because $$5.32-5.3=0.02$$.

• percent error

Percent error is a way to describe error, expressed as a percentage of the actual amount.

For example, a box is supposed to have 150 folders in it. Clare counts only 147 folders in the box. This is an error of 3 folders. The percent error is 2%, because 3 is 2% of 150.