Question 867796: A jet flies from New York to Atlanta at an average rate of 420 mph. On the return trip, there is a strong tail-wind and the plane's speed is 630 mph. What is the average for the round trip?
Answer by jim_thompson5910(35256)   (Show Source):
You can put this solution on YOUR website! Let's say that the distance from New York to Atlanta is 420 miles. This is not true, but for the sake of the problem, let's say it is.
The speed going from New York to Atlanta is 420 mph. So it will take t = D/r = 420/420 = 1 hour for the plane to get there.
Coming back the same distance, it is now going 630 mph. So it will take t = D/r = 420/630 = 2/3 an hour to get back
Overall, the plane has traveled for 1+2/3 = 3/3+2/3 = 5/3 hours.
Also, the plane has gone 420+420 = 840 miles total.
Divide the total distance by the total time to get the overall average speed
r = D/t
r = 840/(5/3)
r = 840*(3/5)
r = 2520/5
r = 504
So the average speed is 504 mph
Note: this works for any distance you pick from NY to Atlanta.
|
|
|
