Puzzle of the day · No. 17 · 29 October
The launderette
A launderette has two washing machines and one dryer. A wash takes 40 minutes, drying takes 60. Lucky has three loads of laundry. What is the shortest time in which he can wash and dry everything?
Answer: 3 hours 40 minutes. The bottleneck is the dryer: three drying cycles in a row take 3 hours, and the first cannot start sooner than 40 minutes in, when a wash finishes. The two machines get the other loads ready while the dryer is busy. 40 + 180 = 220 minutes.
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