# Lesson 14

Percent Error

Let’s use percentages to describe other situations that involve error.

### Problem 1

A student estimated that it would take 3 hours to write a book report, but it actually took her 5 hours. What is the percent error for her estimate?

### Problem 2

A radar gun measured the speed of a baseball at 103 miles per hour. If the baseball was actually going 102.8 miles per hour, what was the percent error in this measurement?

### Problem 3

It took 48 minutes to drive downtown. An app estimated it would be less than that. If the error was 20%, what was the app’s estimate?

### Problem 4

A farmer estimated that there were 25 gallons of water left in a tank. If this is an underestimate by 16%, how much water was actually in the tank?

### Problem 5

For each story, write an equation that describes the relationship between the two quantities.

- Diego collected \(x\) kg of recycling. Lin collected \(\frac25\) more than that.
- Lin biked \(x\) km. Diego biked \(\frac{3}{10}\) less than that.
- Diego read for \(x\) minutes. Lin read \(\frac47\) of that.

### Problem 6

For each diagram, decide if \(y\) is an increase or a decrease of \(x\). Then determine the percentage.

### Problem 7

Lin is making a window covering for a window that has the shape of a half circle on top of a square of side length 3 feet. How much fabric does she need?