Practice!

Sample Problem

To get to your grandparents’ house, you can either bike or drive. You can bike at an average speed of 20 mph, or drive at an average rate of 25 mph. The equations model the distance you are from your grandparents’ house after t hours of travelling by given as Biking: d = -20t + 40 and  Driving: d = -25t + 40. Graph the equations, then see how much time you would save by driving to your grandparent’s house. 

minutes

Solution

Graph two equations:

Biking: d = -20t + 40;  Driving: d = -25t + 40

From the graph, we can see the x-intercepts are (1.6, 0) and (2, 0). This means that by car, you will reach your grandparents’ house in 1.6 hours, and you will reach their house in 2 hours by bike. 1.6 hours in minutes is 96 minutes, and 2 hours in minutes is 120 minutes, which means you will save 24 minutes when you drive instead of bike.