Girl, boy and dog

Found this one on Maths is Fun.

Puzzle

A girl, a boy and a dog are out for a walk. The girl walks at a constant speed of 4 miles per hour, and the boy at a constant speed of 3 miles per hour. The dog, having lots of energy, runs at a constant 7 miles per hour. The dog runs back and forth between the boy and the girl. He looses no time changing direction. After one hour of this, how far as the dog traveled?

Help

Hint

This puzzle sound very difficult, but it really isn't. Don't try to hard.

Answer

The dog traveled a total of seven miles.

Solution

Traveling at 7 miles per hour for one hour means you have traveled 7 miles. A much harder question is to find the dogs net change in position.

References

Maths is Fun - math and logic puzzles appropriate for math education.