A can do 3 piece of work in 4 hours, B and C together in 3 hours , and A and C together in 2 hours. How long will B alone take to do it?

A 8 hours
B 12 hours
C s10hours
D 24 hours

Correct Answer: 12 hours

A,B and C together need = (3×4)/(3 + 4) = 12/7 hours And C need 2 hours ∴B need = {(12/7)×2}/{2 - (12/7)} hours                   = (24/7)/{(14 - 12)/7}                   = 24/2 hours                   = 12 hours 
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