Sandy walks around a circular field at the rate of one round per hour while Molly runs around it at the rate of five rounds per hour. If they start in the same direction from the same point, how many minutes will it take until they meet again?
Choose the most appropriate option.
A) 9	B) 12	C) 15	D) 18	E) 21
Since Sandy and Molly move in the same direction along the circle, they will first meet each other when there is a difference of one round between the two.   The relative speed of Sandy and Molly is   5 - 1= 
<gadget id="calculator">  5 - 1</gadget>
<output>4</output>
4 rounds per hour.   The time required to complete one round at this speed is 1/4 hours= 15 minutes.   The answer is 15.
<result>C</result>
Sandy walks around a circular field at the rate of one round per hour while Molly runs around it at the rate of five rounds per hour. If they start in the same direction from the same point, how many minutes will it take until they meet again?