SOLUTION: Your friend flew to Miami in a plane that averaged 600 mi/h. She drove back home, averaging 50 mi/h. What is her average speed in miles per hour for the whole trip, rounded to the

Question 1081494: Your friend flew to Miami in a plane that averaged 600 mi/h. She drove back home, averaging 50 mi/h. What is her average speed in miles per hour for the whole trip, rounded to the nearest tenth? Assume the distances traveled by the plane and car are equal.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Your friend flew to Miami in a plane that averaged 600 mi/h.
She drove back home, averaging 50 mi/h.
What is her average speed in miles per hour for the whole trip, rounded to the nearest tenth?
Assume the distances traveled by the plane and car are equal.
:
let d = the distance of the plane and the distance of the car
let s = average speed of the trip
Write time equation, time = dist/speed
:
Plane time + car time = total time
+ =
multiply by 600s, cancel the denominators and you have:
ds + 12ds = 600(2d)
13ds = 1200d
divide both sides by d
13s = 1200
s = 1200/13
s = 92.3 mph is the average speed
:
:
Confirm this, find actual times if the distance is 600 mi
600/600 = 1 hr
600/50 = 12 hrs
----------------
1200/92.3 ~ 13 hrs
;
Find the times if the distance is 300 mi
300/600 = .5 hrs
300/50 = 6.0 hrs
-------------------
600/ 92.3 ~ 6.5 hrs
Just to prove that the distance really does not matter

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