One evening some rodent-like animals, Grey Squirrels, Red
Chipmunks, and Water Rats hurried about in their hidden underground
caverns near Boston Common in Boston.
Another rodent, House Mouse, wandered off too far and fell in a
ravine.
The Grey Squirrels, Red Chipmunks, and Water Rats ran over and
tried to think of a way to save poor House Mouse, but no one had a
long enough rope.
Then someone had an idea: If they formed a chain, holding on to each
other, maybe they could reach down the 40 inches to House Mouse.
The Grey Squirrels were all 12 inches high. The Red Chipmunks were
8 inches high. The Water Rats were 4 inches high.
How many different combinations of their lengths would reach 40
inches?