Math
posted by Emme .
A jet flew from Tokyo to Bangkok, a distance of 4800km. On the return trip the speed was decreased by 200km/h. If the difference times of the fights was 2 hours, what was the speed from Bangkok to Tokyo.

time for 1st flight = 4800/x
time for return flight = 4800/(x200)
4800/(x200)  4800/x = 2
multiply by x(x200)
4800x  4800(x200) = 2x(x200)
960000 = 2x^2  400x
x^2  200x  480000=0
(x  800)(x + 600) = 0
x = 800 or x = 600 , the negative speed makes no sense
so x = 800 km/h
check:
1st flight = 4800/800 = 6 hrs
2nd flight = 4800/600 = 8 hrs
difference is 2 hours, YEahh!