Question 1084695
speed*time=distance
x is base speed of plane
x*t=1200
(x-40)(t+(1/3))=1200
so xt=xt+(1/3)x-40t-40/3
0=(1/3)x-40t-40/3; x=1200/t
0=(400/t)-40t-(40/3)
multiply by 3t
0=1200-120t^2-40t
120t^2-40t-1200=0
3t^2-t-30=0
(3t-10)(t+3)=0
t=10/3 hours, only positive root.
x*10/3=1200
10x=3600
x=360 km/h, ANSWER, and it will take 3 1/3 hours to go 1200 km
x-40=320 km/h, and it will take 3 2/3 hours (20 more minutes) to go 1200 km.