Q. 74.8( 6 Votes )

An areoplane takes 1 hour less for a journey of 1200 km if its speed is increased by 100 km / hr from its usual speed. Find its usual speed.

Answer :

Time = distance/speed


Given, areoplane takes 1 hour less for a journey of 1200 km if its speed is increased by 100 km / hr from its usual speed.


Let the usual speed be ‘a’.



1200 ×(a + 100 –a) = a2 + 100a


a2 + 100a – 120000 = 0


a2 + 400a – 300a – 120000 = 0


a(a + 400) – 300(a + 400) = 0


(a + 400)(a – 300) = 0


a = 300 km/hr


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