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First Story: Time
Episode 1 Riddle O'Clock

The following riddle provokes magnificent struggles by readers.

Riddle O'Clock. John lives in an Atlantic Coast state of the United States, and Mary lives in a Pacific Coast state. When talking on the telephone from home, they realized it was the same time in both locations. How could this have been possible?

  Since Eastern time and Pacific time differ by three hours, this puzzle sounds triply difficult. Many readers try to use Alaska or Hawaii somehow, but they are just an hour or two earlier than California, just four or five hours earlier than New York, nowhere near the 12 hours earlier needed to carry them back around the clock to resemble Eastern time. In desperation some readers call Texas an Atlantic coast state or argue for foreign Pacific Coast states such as Mexico, Panama, Columbia, Equador, Peru, or Vietnam. Rest assured that "Math Chat" does not deal in such trickery.

  The first key to the puzzle is that the panhandle of Florida, which is certainly an Atlantic Coast state, extends well into the central time zone. John probably lives in Pensacola, Florida. That's one hour.

  Secondly, one Pacific Coast state extends into the Mountain time zone, not California, not Washington, but Oregon, perhaps to share time with neighbors in Idaho. Mary probably lives in Ontario, Oregon. That's two hours, and John and Mary's clocks are now just one hour apart, as in Figure 4.

  The key to the thirds hour is that daylight saving time ends an hour earlier in the central time zone than in the Mountain time zone. On the last Sunday in October, for the hour following the turn-back from 2 a.m. Central Daylight Time back to 1 a.m. Mountain Daylight Time (MDT), John and Mary would enjoy the same time in both locations.

  An amazing feature of this solution is that it tells us almost exactly where and when this remarkable coincidence occurred: Pensacola, Florida and Ontario, Oregon, on the last Sunday in October, at about 1:30 a.m. (CST=MDT).