Chapter 4: Quadratic Equations

Example 8. A plane left 30 minutes later than the scheduled time and in order to reach the destination 1500km away in time, it has to increase the speed by 250 km/hr from the usual speed. Find the usual speed.

Solution:- Let the usual speed of plane be x km/hr.

The increased speed of the plane = (x + 250) km/hr.

Distance = 1500 km

or,

or, x² + 250x - 750000 = 0

or, x² + 1000x - 750x - 750000 = 0

or, x(x + 1000) -750 (x + 1000) = 0

or, ( x + 1000) ( x - 750) = 0

or, x = -1000, 750

As speed can not be negative

Usual speed = 750 km/hr.