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.
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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