Question 151179
a plane flies 900 miles with a tail wind, in 3 hours. It takes the same plane 4 hours to fly the 900 miles when flying against the wind. What is the planes speed in still air?
:
Let x = speed of the plane
Let y = speed of the wind
then
(x+y) = ground speed with the wind
and
(x-y) = ground speed against the wind
:
Two distance equations:
3(x+y) = 900 (with the wind)
4(x-y) = 900 (against the wind)
:
Simplify; divide the 1st equation by 3, and 2nd equation by 4:
x + y = 300
x - y = 225
-------------addition eliminates y; find x
2x = 525
x = {{{525/2}}}
x = 262.5 mph
:
:
Check solution:
Find the speed of the wind: 262.5 + y = 300; y = 37.5
3(262.5 + 37.5) = 900
4(262.5 - 37.5) = 900