How Do You Calculate the Average Speed for a Round Trip?

[mbayabo]

A car travels along a certain road at an average speed of 42 km/h, and returns along the same road at an average speed of 52 km/h. Calculate the average speed for the round trip, to within 0.1 km/h.

i have no clue. I'm trying to help a friend with general Physics homework (i've taken physics with calc) but i can't get this very simple question. please help!

 

[f95toli]

This thread should be in the homework sub-forum.

Anyway, how long does it take for the car to travel to a destination a distance $x$ away?
How long does it take to get back?

 

[mbayabo]

that wasnt given so idk.

 

[Born2bwire]

It doesn't matter what x is, it should come out the same since we are talking about ratios.

 

[mbayabo]

ok so how do u get it?

 

[ApertureDude]

If its the same distance, then you just need an average of 42 and 52.

42+52=94

94/2= 47km/h

 

[mbayabo]

it's not it. we've tried that. the question is weird. =/

 

[ApertureDude]

A car travels along a certain road at an average speed of 42 km/h, and returns along the same road at an average speed of 52 km/h. Calculate the average speed for the round trip, to within 0.1 km/h.

Hmm, well if that's the EXACT wording of the question, I have no idea. Sorry.