A and B are working on a job. A is twice as efficient as B. If A can finish the job in 30 days, in how many days can B finish the job alone?
Answer: C
Efficiency is inversely proportional to the time taken. If A is twice as efficient as B, A will take half the time B takes. So, Time taken by B = 2 * Time taken by A = 2 * 30 = 60 days.