DAY 215

A man walking a dog along a staraight road spots a friend in the distance. They wave to one another and the dog sprints ahead to greet her. As soon as it arrives, the dog turns around and runs straight back to the man. It then turns again and runs back to the woman, and continues doing this until the man and woman meet. If the man and woman are initially one mile apart, and each walks at a steady pace of 3 miles per hour, and the dog runs at 9 miles per hour, how far does the dog run?

Answer:

1 1/2 miles.............At a combined speed of 6 miles per hour, the man and woman meet in 10 minutes (1/6 hour). At a speed of 9 miles per hour, the dog would cover
a mile and one half (D = 9 x 1/6).