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?
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