A type Q machine can complete a job in 5 hours and a type B machine can complete the job in 7 hours. How many hours will it take 2 type Q machines and 3 type B machines working together and independently to complete the job? Select the correct option.
A) 1 / 5
B) 29 / 35
C) 5 / 6
D) 35 / 29
E) 35 / 12

Rationale: now d should be the answer . q need 5 hours to complete and b needs 7 hours to compete so 2 q + 3 b will complete 2 / 5 + 3 / 7 or 29 / 35 portion of the job in 1 hour so the whole job will take 35 / 29 hours . . . . = d
Answer: D