Author: SEG
Last saved by: MHE
Company: McGraw-Hill

Lesson 1-7

Example 1	Construct a Scatter Plot
HEATING COSTS	The table shows the average monthly outside temperature and the corresponding average monthly heating cost for a two story home during the fall and winter of 2000.  Make a scatter plot of the data.
Temperature (°F) | 58 | 47 | 34 | 28 | 38 | 44
Cost | $51 | $73 | $96 | $145 | $102 | $85

Let the horizontal axis, or x-axis, represent the temperature.  Let the vertical axis, or y-axis, represent the cost.  Then graph ordered pairs (temperature, cost).

Example 2	Interpret Scatter Plots
Determine whether the scatter plot of hours spent studying for a test and test score might show a positive, negative, or no relationship.  Explain your answer.

As the hours spent studying increases, the 
test score will also increase.  So, a scatter 
plot of the data would show a positive relationship.

Example 3	Use Scatter Plots to Make Predictions
GAS MILEAGE	A consumer products group has collected the following data on the relationship between the weight of a car and its average gas mileage.  The table shows the results.

Weight (pounds) | Miles per Gallon
2750 | 29
3125 | 23
2100 | 33
4082 | 18
2690 | 20
3640 | 21
4380 | 14
2241 | 25
2895 | 31
3659 | 17

a.  	Make a scatter plot of the data.

Let the horizontal axis represent weight, and let the vertical axis represent miles per gallon.  Then graph the data.

b.  	Does the scatter plot show a relationship between the weight of a car and its gas mileage?  Explain.

As the weight of the car increases, the gas mileage decreases.  So, the scatter plot shows a negative relationship.

c.  	Predict the gas mileage of a car that weighs 4500 pounds.

By looking at the pattern in the graph, we can predict that the gas mileage of a car weighing 4500 pounds will be about 13 miles per gallon.