Question

Denver is in Mountain Time and Chicago is in Central Time. If it’s $7:00$ P.M. in Denver, what time is it in Chicago?
A. $6:00$ P.M.
B. $8:00$ P.M.
C. $5:00$ P.M.
D. $7:00$ P.M.

Answer 1

Hint: The angular distance east or west of the Prime Meridian of a place is known as its longitude. It is also measured in degrees. The longitudes vary from $0^\circ $ to $180^\circ $ eastward and westward of the Prime Meridian. The part of the earth east of the Prime Meridian is called the eastern hemisphere and in its west, it’s referred to as the western hemisphere.

Complete step-by-step solution:
We all know that the earth rotates over its axis from west to east. It makes the sunrise in the east and set in the west. The rotation of the earth takes 24 hours over its axis to complete one circle or $360^\circ $ of longitudes. The sun thus takes 12 hours’ time to traverse the eastern and western hemispheres as 180° of longitudes fall both east and west of the Prime Meridian. In other words, in every four minutes of time, the sun traverses $15^\circ $ of longitudes per hour or one degree of longitude. Further, the time decreases when we move from west to east and increases with our westward movement. The local time of an area with respect to the time at the Prime Meridian ($0^\circ $ Longitude) is determined by the rate of the time at which the sun traverses over certain degrees of longitudes.
A region of the globe that observes a uniform standard time is called a time zone. And Denver is located in the Mountain Time zone and Chicago in the Central Time zone. Thus, the Central Time zone is one hour ahead of the Mountain Time zone, and the time in Chicago would be 8:00 P.M.
The longitudinal location of Chicago is $87^\circ $ and Denver is $104^\circ $ towards the west.
Thus, the difference between Denver and Chicago is $104^\circ - 87^\circ = 17^\circ $
And we know that $1^\circ $=4 minutes
Thus, the difference between Denver and Chicago=17×4=68 minutes
${\text{Total time difference = }}\dfrac{{68}}{{60}}$ hours
= $1.13$ hour
Thus, the time difference is close to one hour and the time in Chicago would be $8:00$ P.M.

Thus, option (B) is correct.

Note: In the same way, the time may be determined for any place in the world. However, in order to maintain uniformity of time as far as possible within the territorial limits of a country, the Standard Meridian is taken as the time at the central meridian of the country and its local time is taken as the standard time for the whole country.