1. Calculate Relative Error
SWBAT calculate relative error in measuring cubic and square units

2. Definitions Percent of error Relative error
A way to describe how accurate a measure is
Relative error
Another way to describe the extent of error

3. Calculating Percent Error
Subtract the actual value from the measured value
Take the absolute value of this number
Divide it by the actual value
Multiply by 100 to make it a percent
|Measured area – actual area|
actual area
●100

4. Calculating Relative Error
Subtract the actual value from the measured value
Take the absolute value of this number
Divide it by the actual value
|Measured area – actual area|
actual area

5. Example – Fermi’s estimation of Earth’s circumference
Fermi estimated that each time zone in America is about 1000 miles
There are 24 time zones on Earth so he estimated that Earths circumference would be about 24,000 miles
The actual circumference is 24,902. What is his percent error and relative error?

6. Examples Find the percent of error and realtive error of the area
Measured: 42 ½ inches by 68 inches
Actual;: 42 inches by 67 ½ inches
Area formula = A = lw

7. Examples
A store owner measured a shipping box and advertised its dimensions as 30in by 24in by 14in. The actual dimensions of the box were 29 1/2in by 23 1/2in by 13 1/2 in.
What was his percent of error and the relative error?
Volume formula: V = lwh

8. Find percent error and relative error of area
Measured: 5 1/2 yd by 2 3/4yd
Actual: 5 1/4yd by 2 1/2 yd
You try:
Measured: 16m by 11m
Actual: 16.2m by 11.8m

9. Find percent error and relative error of volume
Measured: 2ft by 3.5ft by 7ft
Actual: 2.5ft by 7ft by 4ft
You try:
Measured: 1.2cm by 1.5cm by 2.5cm
Actual: 1.3cm by 2.4cm by 1.5cm

10. In your workbooks Complete pages 281-282, 1-14 Finish for homework
Quiz tomorrow