OlympiadEasyLogic5–6

The Bridge and the Torch

A Ponte e a Lanterna

Four friends must cross a footbridge at night. They share one torch, the bridge holds at most two people at a time, and whoever crosses must carry the torch. Alone they need $1$ , $2$ , $5$ and $10$ minutes; a pair walks at the speed of the slower one. What is the shortest possible total time?

Ask when the two slowest should travel, instead of always sending the fastest as an escort.

Solution

Step 1 of 8

1.Sending the fastest back every time costs $1 + 10 + 1 + 5 + 2 = 19$ minutes.