~ 4.14 ~

Percent error can be used to describe any situation where there is a correct value and an incorrect value, and we want to describe the relative difference between them. For example, if a milk carton is supposed to contain 16 fluid ounces and it only contains 15 fluid ounces:

• the measurement error is 1 oz, and
• the percent error is 6.25% because 1 ÷ 16 = 0.0625.

We can also use percent error when talking about estimates. For example, a teacher estimates there are about 600 students at their school. If there are actually 625 students, then the percent error for this estimate was 4%, because 625 − 600 = 25 and 25 ÷ 625 = 0.04.

1. Instructions to care for a plant say to water it with ¾ cup of water every day. The plant has been getting 25% too much water. How much water has the plant been getting?
2. The pressure on a bicycle tire is 63 psi. This is 5% higher than what the manual says is the correct pressure. What is the correct pressure?
3. The crowd at a sporting event is estimated to be 2,500 people. The exact attendance is 2,486 people. What is the percent error?

Many measuring tapes like this are made out of metal. Some metals expand or contract slightly at warmer or colder temperatures.

A metal measuring tape expands when the temperature goes above 50∘F. For every degree Fahrenheit above 50, its length increases by 0.00064%.

1. The temperature is 100 degrees Fahrenheit. How much longer is a 30-foot measuring tape than its correct length?
2. What is the percent error?