Appropriate Level: Trigonometry
Background: Here is a wonderful photograph:
This picture was taken by an astronaut onboard the Apollo 17 spacecraft in 1972. This was the last manned spaceflight to the moon and the last time someone was far enough away from earth to take a picture like this.
The Question: When the astronaut took this picture, how far from earth was he?
Source: The very nice blog: http://sucolex.blogspot.com/