A is twice as efficient as B and B is thrice as efficient as C. If they together can complete the work in 10 days, in how many days can A alone do it?
Answer: B
Let C's efficiency be x. Then B's is 3x and A's is 2*(3x)=6x. Their combined efficiency is x+3x+6x = 10x. Total work = \(10x \times 10 = 100x\). Time taken by A alone = Total work / A's efficiency = \(100x / 6x = 100/6 = 50/3 = 16.67\) days.