ignoring your trick question (90 mins vs 1.5 hrs) here's an honest answer :)
flying east to west is shorter than west to east? why? headwinds and tailwinds. but for this to really factor in the time of the flight will have to be long (like 7+ hours). if you frequently fly to the far east like HK, SG, Phils, Japan etc, you'll find that returning takes approx an hour longer.
in the southern hemisphere, the opposite is true i.e. flying east to west is shorter.
ignoring your trick question (90 mins vs 1.5 hrs) here's an honest answer :)
flying east to west is shorter than west to east? why? headwinds and tailwinds. but for this to really factor in the time of the flight will have to be long (like 7+ hours). if you frequently fly to the far east like HK, SG, Phils, Japan etc, you'll find that returning takes approx an hour longer.
in the southern hemisphere, the opposite is true i.e. flying east to west is shorter.
scientific explanation here - http://www.aerospaceweb.org/question/dynamics/q0027.shtml