Question

The following table shows the time in various cities when it is 4:00 a.m. in New York.

New York
4:00 a.m.
San Juan
5:00 a.m.
Buenos Aires
6:00 a.m.
Dublin
9:00 a.m.
Rome
10:00 a.m.
Istanbul
11:00 a.m.
Saint Petersburg
12:00 p.m.
Beijing
5:00 p.m.
Osaka
6:00 p.m.

If a flight between two of these cities leaves at 1:30 p.m. on Friday (local time), flies for 16 hours and 30 minutes, and arrives at 2:00 a.m. Saturday (local time), which of the following pairs of cities could the flight go between?
a.
New York and Rome
b.
Saint Petersburg and Beijing
c.
Dublin and San Juan
d.
Osaka and Istanbul

Answer 1

Answer: c. Dublin and San Juan.

Reason: Let offset(city) = city time − New York time (from the table): Dublin = +5, San Juan = +1. With a 1:30 p.m. Fri departure and 2:00 a.m. Sat arrival, the local-time difference is 12.5 hours, so offset(origin) − offset(dest) must equal 16.5 − 12.5 = 4. Dublin − San Juan = 5 − 1 = 4, so the flight can go from Dublin (1:30 p.m. Fri) to San Juan (2:00 a.m. Sat). (Check: 1:30 p.m. Dublin = 8:30 a.m. NY; +16.5 h = 1:00 a.m. NY next day = 2:00 a.m. San Juan.)