1. Example 2 Writing an Algebraic Expression You are riding in a hot air balloon. After traveling 5 miles, the balloon speed changes to 6 miles per hour. HOT AIR BALLOONS a. Write an expression for the total distance after traveling for t hours at 6 mi/h. b. What is the total distance if you travel for 2 hours at 6 mi/h ?

2. Example 2 Writing an Algebraic Expression ANSWER An expression for the total distance is 5 + 6t. b. Substitute for t to find the total distance traveled. 5 + 6 (2) = 17 Substitute 2 for t. ANSWER You travel a total of 17 miles. SOLUTION a. Write a verbal model. 56+t

3. Example 3 Writing an Expression with Two Variables A baseball pitcher’s earned run average (ERA) is calculated by multiplying the quotient of the number of earned runs and the number of innings pitched by 9. BASEBALL a. Write an expression for a pitcher’s ERA. b. Los Angeles Dodger Derek Lowe gave up 89 earned runs in 222 innings pitched. What was his ERA?

4. Example 3 Writing an Expression with Two Variables ANSWER An expression for a pitcher’s ERA is x ÷ y 9. )( SOLUTION a. Write a verbal model. Let x be the number of earned runs and y be the number of innings pitched. y÷ ) 9 ( x

5. Example 3 Writing an Expression with Two Variables ANSWER Derek Lowe’s ERA is about 3.6. b. Substitute for x and y to find Derek Lowe’s ERA. (89 ÷ 222) 9 ≈ 3.6 Substitute 89 for x and 222 for y.

6. for Examples 2 and 3 Guided Practice 5. ANSWER 29 mi WHAT IF? In Example 2, suppose the speed of the balloon changes to 8 mi/h after traveling 5 miles. Find the total distance if the balloon travels at this speed for 3 hours.

7. for Examples 2 and 3 Guided Practice 6. ANSWER 7a + 4c ; $37 CARNIVAL At a carnival, the price of an adult ticket is $7 and the price of a child ticket is $4. Write an expression that gives the total cost of tickets for a adults and c children. Find the total cost of tickets for 3 adults and 4 children.