Jet Plane

A jet plane makes a round trip from Yarmouth to Sydney. When the plane is flying into a headwind during the trip, its speed is 300 km/h, and its speed with a tail wind is 600 km/h. What is the average speed for the round trip?
Source: NCTM Mathematics Teacher, December 2005

SOLUTION
Let d represent the distance in kilometers from Yarmouth to Sydney. If we assume that the trip to Sydney is made up entirely of head wind and that the return trip is made up entirely of tail wind, then the roundtrip flying time equals
\dfrac{d}{300}+\dfrac{d}{600}=\dfrac{3d}{600}=\dfrac{d}{200}
The round trip average speed equals
2d\div\dfrac{d}{200}=400

Answer: 400 km/h

Advertisements

About mvtrinh

Retired high school math teacher.
This entry was posted in Problem solving and tagged , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s