A can do a piece of work in 4 hours; B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it? Answers.
A) 8 hours	B) 10 hours	C) 12 hours	D) 24 hours	E) none of the above

Rationale: "a ' s 1 hour ' s work = 1 / 4 ; ( b + c ) ' s 1 hour ' s work = 1 / 3 ; ( b + c ) ' s 1 hour ' s work = 1 / 2 ( a + b + c ) ' s 1 hour ' s work = ( 1 / 4 + 1 / 3 ) = 7 / 12 b ' s 1 hour ' s work = ( 7 / 12 - 1 / 2 ) = 1 / 12 b alone will take 12 hours to do the work . answer = c"
Answer: C