P is three times as fast as Q and working together, they can complete a work in 9 days. In how many days can Q alone complete the work? Choose the correct choice from the following:
A) 16 days  B) 17 days  C) 19 days  D) 12 days  E) 10 days
P = 3Q   P + Q = 3Q + Q = 4Q   These 4Q people can do the work in 9 days, which means Q can do the work in 48 days.   Hence, P can do the work in 12 days.   Answer:12 days
<result>D</result>
P is three times as fast as Q and working together, they can complete a work in 9 days. In how many days can Q alone complete the work?