Bill travels the 400 miles from San Francisco to Los Angeles at 50 mph. Sam travels the same distance at 40 mph. How many more hours than Bill did it take Sam to travel the 400 miles?
At 50 mph, Bill will travel 400 miles in $\frac{400}{50} = 8$ hours. Sam, on the other hand, traveling at 40 mph, will travel 400 miles in $\frac{400}{40} = 10$ hours. Thus, it took Sam $\boxed{2}$ more hours.