EXAMPLE 1 Describe the correlation of data Describe the correlation of the data graphed in the scatter plot. a. The scatter plot shows a positive correlation between hours of studying and test scores. This means that as the hours of studying increased, the test scores tended to increase. a.

EXAMPLE 1 Describe the correlation of data b. The scatter plot shows a negative correlation between hours of television watched and test scores. that as the hours of television This means that as the hours of television watched increased, the test scores tended to decrease. b.

GUIDED PRACTICE for Example 1 Using the scatter plots in Example 1, predict a reasonable test score for 4.5 hours of studying and 4.5 hours of television watched. 1. Sample answer: 72, 77 ANSWER

Swimming Speeds EXAMPLE 2 Make a scatter plot The table shows the lengths ( in centimeters ) and swimming speeds ( in centimeters per second ) of six fish. a. Make a scatter plot of the data. b. Describe the correlation of the data.

EXAMPLE 2 Make a scatter plot Treat the data as ordered pairs. Let x represent the fish length ( in centimeters ), and let y represent the speed ( in centimeters per second ). Plot the ordered pairs as points in a coordinate plane. SOLUTION a. The scatter plot shows a positive correlation, which means that longer fish tend to swim faster. b.

GUIDED PRACTICE for Example 2 Make a scatter plot of the data in the table. Describe the correlation of the data. 2. ANSWER The scatter plot shows a positive correlation.

BIRD POPULATIONS EXAMPLE 3 Write an equation to model data The table shows the number of active red-cockaded woodpecker clusters in a part of the De Soto National Forest in Mississippi. Write an equation that models the number of active clusters as a function of the number of years since Year Active clusters

STEP 1 SOLUTION EXAMPLE 3 Write an equation to model data Make a scatter plot of the data. Let x represent the number of years since Let y represent the number of active clusters.

STEP 3 EXAMPLE 3 Write an equation to model data STEP 4 STEP 2 Decide whether the data can be modeled by a line. Because the scatter plot shows a positive correlation, you can fit a line to the data. Draw a line that appears to fit the points in the scatter plot closely. Write an equation using two points on the line. Use (2, 20) and (8, 42).

Write slope-intercept form. Find the slope of the line. EXAMPLE 3 Write an equation to model data m = – 20 8 – 2 = 22 6 = y 2 – y 1 x 2 – x 1 = Find the y- intercept of the line. Use the point (2, 20). y =mx + b 20 =(2) + b 11 3 Substitute for m, 2 for x, and 20 for y. 11 3

EXAMPLE 3 Write an equation to model data 38 3 = b Solve for b. An equation of the line of fit is y = 11 3 x The number y of active woodpecker clusters can be modeled by the function y = where x is the number of years since ANSWER 11 3 x

GUIDED PRACTICE for Example 3 3. Use the data in the table to write an equation that models y as a function of x. ANSWER Sample answer: y = 1.6x + 2.3

a. Describe the domain and range of the function. EXAMPLE 4 Interpret a model Refer to the model for the number of woodpecker clusters in Example 3. b. At about what rate did the number of active woodpecker clusters change during the period 1992–2000?

EXAMPLE 4 Interpret a model SOLUTION The domain of the function is the the period from 1992 to 2000, or 2  x  10. The range is the the number of active clusters given by the function for 2  x  10, or 20  y  a. The number of active woodpecker clusters increased at a rate of or about 3.7 woodpecker clusters per year b.

EXAMPLE 4 GUIDED PRACTICE for Example 4 In Guided Practice Exercise 2, at about what rate does y change with respect to x. 4. ANSWERabout 1.6