MediumBrain Teasers

Bridge Crossing

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Four people must cross a bridge at night with one flashlight. They take 1, 2, 5 and 10 minutes to cross. At most two cross at once, and a pair moves at the slower person’s pace; the flashlight must be walked back each time. What is the minimum total time (minutes)?

Approach

Get the two slowest across together.

Use the fastest two as shuttles.