A car is making a 12-mile trip. It travels the first 6.0 miles at 30 miles per hour and the last 6.0 miles at 60 miles per hour. What is the car's average speed for the entire trip?

Question

Quizplus · Accepted Answer

We can use the formula for average speed:
Average speed = total distance ÷ total time
Total distance = 12 miles
Total time = (time for first 6 miles) + (time for last 6 miles)
Time for first 6 miles = distance ÷ speed = 6 miles ÷ 30 mph = 0.2 hours
Time for last 6 miles = distance ÷ speed = 6 miles ÷ 60 mph = 0.1 hours
Total time = 0.2 hours + 0.1 hours = 0.3 hours
Average speed = 12 miles ÷ 0.3 hours = 40 mph

A Car Is Making a 12-Mile Trip