A boy, a girl and a dog go for a 10 mile walk. The boy and girl can walk at 2 mph and the dog can trot at 4 mph.

They also have a bicycle which only one of them (including the dog!) can use at a time.
When riding, the boy and girl can travel at 12 mph while the dog can pedal at 16 mph.

What is the shortest time in which all three can complete the trip?

Too-slow scenario: GIRL bikes 5 miles (in 25 minutes), leaves bike and walks the other 5 miles (in 2 hours), finishing the trip in 2 hours 55 minutes. BOY walks first 5 miles, rides second 5 miles, finishes in 2 hours 55 minutes. DOG trots the whole way and finishes in 2 hours 30 minutes.

Improvement: GIRL rides a little farther before she leaves the bike. DOG takes the bike back a short distance. BOY gets on bike sooner. I haven't calculated how far back the dog should take the bike in order to finish at the same time as the humans.

Posted by dave domingo on 2004-02-03 14:19:34