A mathematician is flying non-stop from Edmonton to Frankfurt with
AirTransat. The scheduled flying time is nine hours.
Some time after taking off, the pilot announces that one engine had to
be turned off due to mechanical failure: "Don't worry - we're safe. The
only noticeable effect this will have for us is that our total flying
time will be ten hours instead of nine."
A few hours into the flight, the pilot informs the passengers that
another engine had to be turned off due to mechanical failure: "But
don't worry - we're still safe. Only our flying time will go up to
Some time later, a third engine fails and has to be turned off. But the
pilot reassures the passengers: "Don't worry - even with one engine,
we're still perfectly safe. It just means that it will take sixteen
hours total for this plane to arrive in Frankfurt."
The mathematician remarks to his fellow passengers: "If the last engine
breaks down, too, then we'll be in the air for twenty-four hours
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