# A six-passenger plane cruises at 180 mph in calm air....

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#### Guest

##### Guest
A six-passanger plane cruises at 180 mph in calm air. If the plane flies 7 miles with the wind in the same amount of time as it flies 5 miles against the wind, then what is the wind speed?

#### Mrspi

##### Senior Member

Caron said:
A six-passanger plane cruises at 180 mph in calm air. If the plane flies 7 miles with the wind in the same amount of time as it flies 5 miles against the wind, then what is the wind speed?
Let w = wind speed

Flying with the wind, the plane's speed will be increased by the wind's speed, and the plane will fly at 180 + w mph. Since distance / rate = time, the time it takes for the plane to fly 7 miles at 180 + w mph is 7 / (180 + w) hours.

Flying against the wind, the plane's speed will be decreased by the wind's speed, and the plane will fly at 180 - w mph. The time it takes for the plane to fly 5 miles at 180 - w mph is 5 / (180 - w) hours.

Now, we are told that those two times are equal. So,

7 / (180 + w) = 5 / (180 - w)

Can you finish it now?

#### tkhunny

##### Moderator
Staff member
This is an example of why we don't post things twice. Spending time on answers that already have been given is very irritating.