Monday, December 5, 2011

What was the speed of the jet plane in still air?

A jet plane took off for a 7,956-km journey against the 120-kph wind to another airport. It took the plane 2 hours and 24 minutes less time in returning than in going.|||No. of hours going (t) in terms of speed (x):


t = 7,956/(x - 120)





t = 7,956/(x + 120) + 2.4


t = (7,956 + 2.4x + 288)/(x + 120)


t = (8,244 + 2.4x)/(x + 120)





Speed鈥攛:


(x - 120)(8,244 + 2.4x) = 7,956(x + 120)


8,244x + 2.4x虏 - 989,280 - 288x = 7,956x + 954,720


2.4x虏 = 1,944,000


x虏 = 810,000


x = 900





Answer: 900 kph is the speed of the plane.|||t1 = 7956/(v + 120)





t2 = 7956/(v - 120)





t2 - t1 = 2 hours and 24 minutes = 2.4 hrs





7956/(v - 120) - 7956/(v + 120) = 2.4





v = 900 kph

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