Q. If A and B together can complete a piece of work in 15 days and B alone in 20 days, then in how many days can A alone complete the work ?
Answer: 60 days
Notes: (A + B)'s 1 day's work $latex = \frac{1}{15}&s=1$ B's 1 day's work $latex = \frac{1}{20}&s=1$ ∴ A's 1 day's work $latex = \frac{1}{15}-\frac{1}{20} = \frac{4-3}{60}= \frac{1}{60}&s=1$ ∴ A alone will do the work in 60 days. Hence option [D] is correct answer.

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