The Bridge at Night
Four people must cross a bridge at night with one flashlight; at most two can cross at a time, and any crossing party moves at the slower member's pace. Their individual crossing times are 1, 2, 5, and 10 minutes, and the flashlight must be walked back (never thrown). What is the minimum total time, in minutes, for all four to cross?
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Source: Classic river-crossing timing puzzle in wide circulation; no traceable original source. Statement written for AxiomIQ.