In this activity you will investigate the amount of money earned by Joe, a plumber in New York City, and Tony, Joe's helpful assistant. Joe earns $40 an hour and Tony earns $25 an hour. One day Tony started work at 8 a.m., and Joe started at 10 a.m.

1. By 9 a.m., how much money did Tony earn?                       
     By 9 a.m., how much money did Joe earn?                    

2. By 10 a.m., how much money did Tony earn?                    
     By 10 a.m., how much money did Joe earn?                    

3. By 11 a.m., how much money did Tony earn?                    
     By 11 a.m., how much money did Joe earn?                    

4. Joe and Tony continued to work until 4 p.m. and then quit for the day. Fill in the table below to show the number of hours worked and the number of dollars earned by Tony and Joe.

5. A quantity that varies in a situation is called a variable. Here, time is a variable. Name some other variables.

6. A quantity that remains the same is called a constant. Name some constants in this activity.

7. a. After Tony worked 4 hours, how many hours did Joe work?                    
     b. After Tony worked 6 hours, how many hours did Joe work?                    
     c. Assume both Tony and Joe worked late and put in overtime. How many hours would Joe have worked if Tony worked 10 hours?                    

8. a. How can you determine the earnings of Tony from the number of hours worked?
    b. How can you determine the numbers of hours worked by Joe if you know the numbers of hours worked by Tony?
    c. What is a rule to determine Joe's earnings from the number of hours Joe worked?
    d. What is a rule to determine Joe's earnings from the number of hours Tony worked?  (Hint: the rule has two parts.)

9. a. Who made more money after Tony worked 4 hours?                    
     b. Who made more money after Tony worked 8 hours?                    

10. Predict the time at which Tony and Joe made the same amount of money.