An ordinary plane leaves an airport and flies due west at 180kph. Two hours later, a jet leaves the same airport and flies due west at 900kph. How far from the airport will the jet overtake the ordinary plane?

Answer 1

key point:
at the "overtaking" they both will have gone the same distance in a time 2 hrs apart.

let the time taken by the jet be t hrs
then the time taken by the small plane be t+2 hrs

900t = 180(t+2)
900t = 180t + 360
720t = 360
t = 1/2

then 900t = 450
they will be together after 450 km

check:
jet went 900(1/2) = 450 km
small plane went 180(2 1/2)
= 180(5/2) = 450 km
Ok !