The Rope Bridge

The torch-and-bridge puzzle as a story: speeds of 1, 2, 5 and 10, and a storm 17 minutes out.

Four friends reach a gorge at night with one torch. The bridge holds at most two people, whoever is on it must have the torch, a pair moves at the slower walker's pace, and the torch cannot be thrown back. Their crossing times are 1, 2, 5 and 10 minutes, and the storm hits in 17. The story asks for the minimum time to get all four across. You lock in a guess, then step through the answer and breakdown.

Why quant interviews test this

Interviewers watch for the moment you question the greedy assumption: computing 19, noticing it misses 17, and hunting for overlapped cost is the optimisation instinct being tested. The written solution is at /brain-teasers/bridge-crossing/solution.

The The Rope Bridge guide covers how scoring works, the strategy that wins, a worked example and the mistakes most players make.

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