© Nuffield Foundation 2011 Nuffield Free-Standing Mathematics Activity Plumber’s call-out

© Nuffield Foundation hour Plumber Call-out £20 Hourly rate £40 How much will it cost if the plumber takes 2 hours?

© Nuffield Foundation 2011 The plumber charges £ 20 + £40 per hour. It costs £20 before she does anything. It costs £100 for a 2 hour job. What amounts should go in the gaps in the table? Hours Charge (£) Charge (£) Plumber's charges Hours

Plumber’s call-out At the end of the activity Why was the plumber’s charge not directly proportional to the time she worked? How can you tell from the graph that it is not directly proportional? What does the intercept tell you about the plumber’s charge? What does the gradient tell you? What are the advantages of using a graph to find charges for jobs? What are the disadvantages?