SOLUTION: A car travels up a hill at a constant speed of 36 km/h and returns down the hill at a constant speed of 70 km/h. Calculate the average speed (in km/h) for the round trip.

Click here to see ALL problems on Travel Word Problems

Question 260796: A car travels up a hill at a constant speed of 36 km/h and returns down the hill at a constant speed of 70 km/h. Calculate the average speed (in km/h) for the round trip.

Found 2 solutions by ankor@dixie-net.com, ptaylor:
Answer by ankor@dixie-net.com(22740) (Show Source):
You can put this solution on YOUR website!
A car travels up a hill at a constant speed of 36 km/h and returns down the hill at a constant speed of 70 km/h.
Calculate the average speed (in km/h) for the round trip.
:
Let s = average speed for the round trip
Let d = distance one way;
write a time equation: time = dist/speed
+ =
Multiply equation by by 2520s (36*70) to get rid of the denominators, results:
70ds + 36ds = 2520(2d)
106ds = 5040d
Divide both sides by d
106s = 5040
s = 5040/106
s = 47.5 km/hr, average speed for the round trip

Answer by ptaylor(2198) (Show Source):
You can put this solution on YOUR website!

Distance (d) equals Rate(r) times Time(t) or d=rt; r=d/t and t=d/r
Average Speed(or rate)=(Total Distance)/(Total Time)
Let d=distance up the hill and d=distance down the hill
Time to travel up the hill =d/36
Time to travel down the hill=d/70
Total time=(d/36 + d/70)=(35d+18d)/1260=53d/1260
Total distance=2d
So, Average speed=2d/(53d/1260)=
Average Speed=2*1260*d/53d=2520/53=47.54 km/hr
Hope this helps---ptaylor