An airplane flew for 4 hours with a 20-km/h tail wind. The return flight against the same wind took 5 hours. Find the speed of the plane in still air.
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jessica
ANSWERS: 2
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this is a d=rt problem (distance = rate*time). the distance is the same in both cases, so you have two equations with r being unknown. d1 = r1t1 d2 = r2t2 since d1=d2; r1t1 = r2t2 you know t1 and t2, and you have some info about r, the rate (though you should figure this out on your own). solve for r.
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Let v be the speed of the plane. On the way, the speed of the plane though the air is v. The speed of the air is 20. The ground speed of the plane is v + 20 On the way back the ground speed is v - 20 Distance = speed times time both ways: (v+20) * 4 = (v-20) * 5 80 = v-100 180 = v distance must have been 800km
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