Question

An aeroplane takes off 30 minutes later than the scheduled time and in order to reach its destination 1500 km away in time , it has to increse its speed by 250km/h from its usual speed . Find its usual speed .
A. 1000 km/h
B. 750 km/h
C. 850 km/h
D. 650 km/h

Answer 1

Correct Answer - B
Let the usual speed of the aeroplane be x km/h
Then , `(1500)/(x) - (1)/(2) = (1500)/((x + 250))`
`implies (1500 x + 750000- 1500 x)/(x ( x + 250)) = (1)/(2)`
`implies 750000 = x^(2) + 250 x or x^(2) + 250 x - 750000 = 0`
`implies x^(2) + 1000 x - 750 x - 75000 = 0`
`implies (x + 1000) (x -750) = 0 implies x = 750 , - 1000`
Speed cannot be negative
We get x = 750 km/h