A can work twice as fast as B. A and C together can work three times as fast as B. If A, B
and C complete a job in 30 days working together, in how many days can each of them complete the work.
The correct option is B.
Let the efficiencies of A ,B and C are a,b and c respectively .
   a :b = 2: 1  ....(1)
  ( a + c) : b = 3 : 1    ....(2)
 Comparing eq (1) and (2) we get a= 2 , b=1 and c = 1
 Total work = total efficiency x total time
         = 4 x 30 = 120 unitsÂ
A alone does complete work in $$\frac{120}{2}$$ = 60 days.
 B alone does complete work in $$\frac{120}{1}$$ = 120 days.
 C alon does complete work in $$\frac{120}{1}$$ =  120 days.
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