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If A and B together complete a work in 12 days and B alone can do it in 20 days, how many days will A alone take to complete the work?

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If A and B together complete a work in 12 days and B alone can do it in 20 days, how many days will A alone take to complete the work? Answer: 30 days

Let's denote A's rate of work as A, and B's rate of work as B. Given A + B together complete the work in 12 days: (A + B)'s 1 day's work = 1/12 B alone completes the work in 20 days: B's 1 day's work = 1/20 A's 1 day's work = (A + B)'s 1 day's work - B's 1 day's work = 1/12 - 1/20 = (5 - 3) / 60 = 2 / 60 = 1 / 30 A alone will complete the work in 30 days.

Question context

This question is part of 📏 Arithmetic Aptitude within the broader 🧠 Aptitude Mastery subject and appears in the ASF Airports Security Force preparation collection. Reviewing the answer together with nearby questions helps reinforce the underlying concept and identify how it may appear in competitive exams.