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 choice from the following choices:  A) 8 hours  B) 10 hours  C) 12 hours  D) 24 hours  E) None of these
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 12 hours
<result>C</result>
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 ?