Question

Jo drives 80 miles at an average speed of 50mph. She then travels the next 30 miles at an average speed of 40 mph. She says that the average speed of the total journey is 45mph. Show that Jo is incorrect.

Answer 1

The average speed is 46.8mph

Explanation:

See the attached worksheet. The time travelled for each segment can be calculated by dividing the distance travelled by the average speed for that distance. The two times are 1.60 and 0.75 hours. The total distance travelled is 110 miles. The average for the whole trip would be (110 miles)/(2.35 hours) or 46.8 mph,

Answer 2

Explanation:

To calculate the average speed of a journey, we use the formula: average speed = total distance ÷ total time. Jo travelled 80 miles at 50mph and 30 miles at 40mph, for a total distance of 110 miles. The total time taken was 2.35 hours. Therefore, the average speed of the journey was 46.81 mph, which is higher than Jo's claim of 45mph.