Question

A plane left 30 minutes later than the schedule time . In order to reach its destination 1500 km away in time , it has to increase the speed 10 km/ h. Find its actual speed.

Answer 1

Let the usual speed of the plane be xkm/hr.

Increased speed of the plane = (x + 250) km/hr

Time taken to reach the destination at usual speed,

Time taken to reach the destination at increased speed,

Given, t 1 – t 2 = 30 min

Thus, the usual speed of the plane is 750 km/hr.

Answer 2

Solution :-

Let the original speed of train be x km/hr
New speed = (x + 100) km/hr

We know that,
Time = Distance / Speed

Given : A plane left 30 minutes or 1/2 hours later than the scheduled time.

According to the question,

=> 1500/x - 1500/(x + 100) = 1/2
=> (1500x + 15000 - 1500x)/x(x + 100) = 1/2
=> 2(15000) = x(x + 100)
=> 30000 = x² + 100x
=> x² + 100x - 30000 = 0
=> x² + 600x - 500x - 30000 = 0
=> x(x + 600) - 500(x + 600) = 0
=> (x - 500) (x + 600) = 0
=> x = 500 or x = - 600

∴ x ≠ - 600 (Because speed can't be negative)


Hence,
Its usual speed = 500 km/hr