Lisa and Sarah were given a word problem to work on:
The distance between City A and City B is 360 miles. A car was going at 60 miles per hour from City A to City B; on the way back, the car was going at 40 miles per hour because it was raining really hard so that driver could not see very well. What was the average speed of the car for the round trip?
This was Lisa’s answer:
(60+40)÷2=50 miles per hour
Sarah said: “No, you cannot solve the problem like that. This is how to solve it.”
This was Sarah’s answer:
The total distance for the round trip: 360×2=720 miles
The amount of time the car used to travel from City A to City B:
The amount of time the car used to travel back to City A from City B:
The total amount of time for the round trip:
The average speed for the round trip= the total distance for the round trip÷ the total amount of time spent on the round trip= 720÷15=48 miles per hour
Friends, I believe that you all think that Sarah is right and she is. Remember: when you solve a word problem on travelling, finding the average speed is not the same as finding the average age, the average height, etc.