Math Question

[Jen1129]

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A person travels to work at an average speed of 40 mph and returns home at 60 mph. Which of the following, in mph, is the average speed for the entire trip?
A. 45
B. 46
C. 48
D. 52
E. 54

The correct answer is 48. Can someone please explain to me how to get this answer?

 

[3rdMolarRoller]

Easist way:

the numbers you have to work with are 60 and 40. Look for a number they both can go into easily...24

So lets say the guy has to travel 24 miles to work each way. In the morning he does 40mph and takes him .6 hours (24miles/40mph= .6 hours). In the afternoon he does 60 mph and the 24 mile trip takes .4 hours (24miles/60mph= .4hours). So his total travel time is 1 hour (.4 one way + .6 the other way). In that one hour he traveled a total of 48 miles (24 miles to work + 24 miles back home) and since total driving time is 1 hour...hence avg speed 48MPH

 

[DrTacoElf]

Yeah for these ALWAYS pick a distance to work with. Just make one up 🙂

 

[Dr. Steve Brule]

Easist way:

the numbers you have to work with are 60 and 40. Look for a number they both can go into easily...24

So lets say the guy has to travel 24 miles to work each way. In the morning he does 40mph and takes him .6 hours (24miles/40mph= .6 hours). In the afternoon he does 60 mph and the 24 mile trip takes .4 hours (24miles/60mph= .4hours). So his total travel time is 1 hour (.4 one way + .6 the other way). In that one hour he traveled a total of 48 miles (24 miles to work + 24 miles back home) and since total driving time is 1 hour...hence avg speed 48MPH

that's a good method except i think it's a bit easier (if u don't want to deal with decimals) to use a number like 120..if he has to travel 120mi each way then that's 3 hours on the way there and 2 hours on the way back..so u just divide the total distance by the total time which gives u 240/5 = 48 👍

 

[Jen1129]

Thanks! That definitely helped!