An airplane travels 3900 km at 810 km/h, and then encounters a tailwind that boosts its speed to 950 km/h for the next 3000 km. What was the average speed of the plane for this trip?
3900+3000
6900
6900/8
862.5
It goes 6900 km
the time is 3900/810 + 3000/950
so
Vaverage = 6900 / [ 390/81 + 300/95 ]
= 865.4