Working alone, printers X, Y, and Z can do a certain printing job, consisting of a large number of pages, in 16, 12, and 8 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?	Choose the correct option.
A) 5 / 2 B) 7 / 4 C) 8 / 5 D) 10 / 3 E) 12 / 5

Rationale: the time it takes printer x is 16 hours . the combined rate of y and z is 1 / 12 + 1 / 8 = 5 / 24 the time it takes y and z is 24 / 5 the ratio of times is 16 / ( 24 / 5 ) = 5 * 16 / 24 = 10 / 3 the answer is d .
Answer: D