Question

An airplane departs from LA and flies to NY every 30 minutes. The trip takes 5 hours and 5 minutes. An airplane takes off from NY at the same time that one takes of from LA and flies to LA at the same speed. How many planes does it pass going in the opposite direction?.

Answer 1

Explanation:

If an airplane departs from LA and flies to NY every 30 minutes, then in 5 hours and 5 minutes, or 305 minutes, there will be 305/30 + 1 = 11 airplanes flying from LA to NY (the extra "+1" represents the first airplane that took off at the beginning of the 5 hours and 5 minutes).

Since the airplane that took off from NY flies to LA at the same speed, it will cover the same distance as the LA-NY flight, and it will take the same amount of time. Therefore, it will also pass 11 airplanes going in the opposite direction, as each of those 11 airplanes will be 1/11th of the way through their trip at the same time the NY-LA airplane passes them.

So the answer is 11 airplanes.