If 50 apprentices can finish a job in 4 hours, and 30 journeymen can finish the same job in 6 hours, how much of the job should be completed by 10 apprentices and 15 journeymen in one hour?  Pick:
A) 1 / 9 B) 29 / 180 C) 26 / 143 D) 2 / 15 E) 39 / 121

Rationale: 50 apprentices can finish the job in 4 hours , thus : 10 apprentices can finish the job in 4 * 5 = 20 hours ; in 1 hour 10 apprentices can finish 1 / 20 of the job . 30 journeymen can finish the same job in 4,5 hours , thus : 15 journeymen can finish the job in 6 * 2 = 12 hours ; in 1 hour 15 journeymen can finish 1 / 12 of the job . therefore , in 1 hour 10 apprentices and 15 journeymen can finish 1 / 20 + 1 / 12 = 2 / 15 of the job . answer : d .
Answer: D