X can do a piece of work in 8hours. Y and Z together can do it in 6 hours, while X and Z together can do it in 4 hours. How long will Y alone take to do it? Choices:
A) 24 hours
B) 20 hours
C) 34 hours
D) 12 hours
E) 10 hours

Rationale: x ' s 1 hour work = 1 / 8 ( y + z ) ' s 1 hour work = 1 / 6 ( x + z ) ' s 1 hour work = 1 / 4 ( x + y + z ) ' s 1 hour work = ( 1 / 8 + 1 / 6 ) = 7 / 24 y ' s 1 hour ' s work = ( 7 / 24 - 1 / 4 ) = 1 / 24 y alone will take 24 hours to do the work . correct option is a
Answer: A