If an airplane travels in one direction half of the time at 55km/h ,and the other half at 90km/h.
What is the total distance traveled by the airplane?
It just seems that it does not give you enough information ,but the teacher says there is a way.
Let's denote the total flight time by T and the traveled distance by D. Then
D = (T/2)*55[km/h] + (T/2)*90[km/h].
Here we can find D:
D = T(55+90)/2.
As we see, there is no other way to find traveled distance then to know the total elapsed time.