Numerical answer
Machine A can finish a printing job alone in 15 days and machine B alone in 10 days. Both machines run together for 3 days, after which machine A breaks down and machine B completes the rest of the job alone. How many more days does machine B need (in days)?
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Answer: 5
A's rate = 1/15, B's rate = 1/10 per day. Combined rate = 1/15+1/10 = 2/30+3/30 = 5/30 = 1/6. Work done in 3 days = 3×1/6 = 1/2. Remaining work = 1 − 1/2 = 1/2. Time for B alone to finish the remaining half = (1/2) ÷ (1/10) = 5 days.
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