Consider the following: Three men want to cross a river; they find a boat, but it is a very small boat. It will only carry 200 pounds. The men are named Large (200 lbs), Medium (120 lbs), and Small (80 lbs)

How can they all get across? They might have to make several trips in the boat (VanLehn, 1989).
a. two trips
b. three trips
c. five trips
d. cannot be done (evidence for the importance of searching for contradictions)

Answer: c