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 2 hours.How long will B alone take to do it ? Choose the correct option
A) 8 hours
B) 10 hours
C) 12 hours
D) 24 hours
E) none of these

Rationale: "solution a ’ s 1 hour ’ s work = 1 / 4 ; ( b + c ) ' s 1 hour ’ s work = 1 / 3 ; ( a + 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