Q. At a certain place, the Greenwich Mean Time is ahead by 12 hours. The place is located at which of the following locations?
Answer: 180°W of GMT
Notes: A traveler going eastwards gains time from Green­wich until he reaches the meridian 180°E, when he will be 12 hours ahead of G.M.T.
Similarly, in going westwards, he loses 12 hours when he reaches 180°W. There is thus a total difference of 24 hours or a whole day between the two sides of the 180° meridian.
This is the International Date Line where the date changes by exactly one day when it is crossed. A traveler crossing the date line from east to west loses a day and while crossing the dateline from west to east he gains a day.