Question: Working alone, Printers X, Y, and Z can do a certain printing job, consisting of a large number of pages, in 12, 20, and 20 hours, respectively. What is the ratio of the time it takes Printer X to do the job, working alone at its rate, to the time it takes Printers Y and Z to do the job, working together at their individual rates?
Options:
(A)  4/11
(B)  1/2
(C)  15/22
(D)  10/1
(E)  11/4 Let's think first. Some random reasoning:
user
P1 takes 12 hrs
Rate for P2P3 together = 1/20 + 1/20 = 1/10
Therefore they take 10
Ratio = 10/1 = The final answer: (D).
assistant