A plane left 30 minutes later than the scheduled time and in order to reach the desination, 1500km away in time. It has to increase the speed by 100km/h from the usual seed. Find the usual speed?
Answers
Given:
Late = 30 min
Distance = 1500 km
Speed increase = 100 km / hr
To find:
The usual speed.
Solution:
By formula,
Speed = Distance / Time
Since the time is unknown,
Consider x for time,
Speed original = 1500 / x
Time taken = ( x - 1 / 2 )
Therefore,
Substituting the value of x,
Speed new = 1500 / (x - 1/2)
Speed New - Speed original = 100
( 1500 / ( x - 1 / 2 ) ) - ( 1500 / x ) = 100
150 ( ( 10 / x - 1 / 2 ) - 10 / x = 100
30 x -30 x +15 = 2x^2 - x
15 = 2x^2 - x
2x^2 - x -15 = 0
Solving,
x = -5/2
x = 3
As time cannot be negative,
The usual time taken by the plane is 3 hr
Speed original = ( 1500 / 3 ) = 500 km / hr
Hence, the usual speed of the plane is 500 km / hr
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