The Cassette Recorder

Four people must cross a rickety bridge at night.

Unfortunately, they have only one torch and the bridge is too dangerous to cross without one.

The bridge can only hold two of them at a time.

The four people cross at different speeds: Times for each person: 1 minute, 2 minutes, 7 minutes and 10 minutes.

What is the shortest time in which they can all cross?

Ah! Click here to read the solution.

1 and 2 minute-person cross first

2 minute-person comes back

7 and 10 minute-person go across the bridge

1 minute-person comes back

Finally, 1 and 2 minute-person cross the bridge (voilà)

Total time (shortest) = 2 + 2 + 10 + 1 + 2 = 17 mins. 🙂

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