Two horses begin running on an oval course at the same time. One runs each lap in 4 minutes; the other takes 12 minutes to run each lap. How Many minutes after the start will the faster horse have a one lap lead?
Choose the correct choice from the following answers:
A) 36
B) 12
C) 9
D) 4
E) 6
The rate of the faster horse is 1/4 lap/minute;   The rate of the slower horse is 1/12 lap/minute;   Their relative rate is 1/4-1/12=1/6 lap/minute;   The faster horse to gain one full lap will need time=distance/rate=1/(1/6)= 
<gadget id="calculator">1/(1/6)</gadget>
<output>6</output>
6 minutes.   Answer: 6.
<result>E</result>
Two horses begin running on an oval course at the same time. One runs each lap in 4 minutes; the other takes 12 minutes to run each lap. How Many minutes after the start will the faster horse have a one lap lead?