A plane travels 1200 km distance in 12 hrs with the wind The

A plane travels 1200 km distance in 12 hrs with the wind. The return trip against the wind takes 15 hrs. Find the rate of the plane in still air.

Solution

d = rt
d = (r+w)*12
d = (r-w)*15
12(r+w) = 15(r-w)
12r+12w = 1200 --> r+w = 100
15r-15w = 1200 --> r-w = 80
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r+w = 100
r-w = 80
---------- Add
2r = 180
r = 90 kph
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The rate is called the airspeed, not \"the speed in still air.\"
The airspeed plus the effect of the wind is the groundspeed.
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Airplanes don\'t use kilometers, they use knots for speed.
1 knot = 1 nautical mile per hour. Ships also use knots.
Speed is knots, not knots per hour.