Question

A plane left 30 minutes late than it's scheduled time and in order to reach the destination 1500 km away in time, it had to increase it's speed by 100 km/h from the usual speed. Find it's usual speed.​

Answer 1

Let the usual speed of the plane = x km/hr

Distance to the destination = 1500 km

Increased speed = 100 km/hr

So, according to the question

1500/x - 1500(x+100) = 30/60

x2 + 100x - 300000 = 0

x2 + 600x - 500x - 300000 = 0

(x + 600)(x - 500) = 0

x = -600 or 500

Since, speed can not be negative, x = 500

Usual speed of plane is 500 km/hr.