Question

How far from an airport can an airplane fly and return in 8 hours, if it's outgoing speed is 160 km per hour and it's returning speed is 240 km per hour

Answer 1

speed = distance/time
total time is 8 hours

outgoing speed is 160 km per hour, 
so time = d/160

returning speed is 240 km per hour,
so time = d/240

 d/160 + d/240 = 8

3d/480 + 2d/480 = 8
5d/480 = 8
5d =480 (8)
5d = 3840
d=3840/5
d=768

answer: so the distance is 768 km

Answer 2

T = 8 h
v1 = 160 km/h
v2 = 240 km/h

mmc 160 e 240 = 80
s = 80*8
s = 640 km