You know the six time zones. Now use them to figure out the time somewhere else. You will use what you know about elapsed time.
Key idea
Count the zones between the two places. Going east, add one hour for each zone. Going west, subtract one hour for each zone.
Why it works
Why does this work? All the clocks move together: when one gains an hour, they all do. The zones only shift the starting point. So the difference between two places stays the same all day: Denver is always 2 hours behind Atlanta (when both follow the same daylight saving rules).
Worked example: Going east
In January, it is 4:30 p.m. in Seattle. What time is it in Atlanta?
- Seattle is Pacific; Atlanta is Eastern.
- Pacific to Mountain to Central to Eastern: 3 zones east.
- East is later, so add 3 hours: 4:30 p.m. + 3 = 7:30 p.m.
Answer: 7:30 p.m.
Worked example: A flight west
A plane leaves Chicago at 10:00 a.m. and flies 4 hours to Los Angeles. What time is it in Los Angeles when it lands?
- On Chicago's clock, it lands at 10:00 a.m. + 4 hours = 2:00 p.m.
- Los Angeles is 2 zones west of Chicago (Central to Mountain to Pacific).
- Subtract 2 hours: 12:00 noon.
Answer: 12:00 noon in Los Angeles.
Common mistake
The most common slip is adding when you should subtract. Check yourself with the Sun: the Sun rises in the East first, so the East is always ahead. If your answer makes a western city later than an eastern one, flip it.
In this topic, problems say "in January" so that every state is on standard time. In summer, Arizona and Hawaii do not change their clocks; the next topic shows what that does.