# math

posted by joy

When an airplane flies with a given wind, it can travel 3000 km in 5hrs. When the same airplane flies in the opposite direction against the wind it takes 10hrs to fly the same distance. Find the speed of the plane in still air and the speed of the wind.

1. Reiny

speed of plane in still air --- x km/h
speed of wind ---- y km/h

speed of plane with the wind --- x+y km/h
speed of plane against the wind -- x-y km/h

first fact:
5(x+y ) = 3000
x+y = 600 #1 equation
second fact:
10(x-y) = 3000
x-y = 300 #2 equation

add #1 + #2, it becomes so easy.

2. joy

speed of a plane in still air is 450
speed of wind is 150

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