Question

Due to some technical problems, an aeroplane started late by one hour from its starting point.The pilot decided to increase the speed of the aeroplane by 100km/hr from its usual speed , to cover a journey of 1200km in time .Find the usual speed of the aeroplane.

Answer 1

Solution:-
Let the original speed be 'x'
Original time taken (OT) = 1200/x
New time (NT) = 1200/x+100
According to the question
OT - NT = 1
1200/x - 1200/x+100 = 1
1200/(x+100) - 1200x/x²+100x = 1
1200x+120000 - 1200x/x²+100x = 1
120000 = x²+100x
x²+100x-120000 = 0
x²+400x-300x-120000 = 0
x(x+400) - 300(x+400) = 0
(x+400) (x-300) = 0
x = -400
x = 300
Speed cannot be negative.
Therefore, x= 300
The speed is 300 km/hr Answer.


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