Mary and Jimmy start running from the same spot, but in opposite directions. Mary runs at 5 miles per hour and Jimmy runs at 4 miles per hour. What is the distance between them after 1 hour? Let's be accurate as possible.
In 1 hour, Mary will have traveled 5 miles / hour * 1 hour = 5 miles. In 1 hour, Jimmy will have traveled 4 miles / hour * 1 hour = 4 miles. Since they are running in opposite directions, the distance between them will be 5 miles + 4 miles = 9 miles.
The answer: 9.