At what time?
A plane flies from Athens to Brussels at maximum speed. Normally, flying at maximum speed would enable it to reach Brussels in four-fifths of the time that it takes to fly there at cruising speed. On this occasion, however, the velocity of a favorable wind enables it to get there in only half the time it would normally take at maximum speed. On the return journey, it leaves Brussels at 1 p.m. Ignoring time zones, and encountering the same velocity and direction of wind, at what time will the plane arrive back at Athens?
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Never! Most of the information given is irrelevant. If the tails wind doubled its speed going, its velocity must have equaled that of the plane. On the way back, such a wind would effectively reduce the speed of the plane to zero.