# An airplane flew 4 hours with a 25 mph tail wind. The return trip against the same wind took 5 hours. How do you find the speed of the airplane in still air?

##### 2 Answers

The speed of the plane is 225 mph.

#### Explanation:

To solve this task you can use the following system of equations:

Both equations come straight from the laws of cinematics (time equals distance divided by speed)

If you multiply both equations by the denominators you will get:

So you can write only one equation with the unknown

**Answer:** The speed of the plane without the wind is

**Check:**

First we calculate the distance:

Next we check the times:

a) with the wind

b) against the wind

I found

#### Explanation:

Call the speed of the plane (in still air)

and:

from the first equation:

substitute into the second: