An aeroplane covers 2500 km, 1200 km and 500 km at the rate of 500 km/hr, 400 km/hr and 250 km/hr respectively. Find its average speed for the whole journey.
A bus covers 100 km in first 2 hours, 64 km in the next 1 hour and 72 km in the next 2 hours. Find the average speed of the bus during the whole journey.
A car covers a certain distance in 50 minutes if it runs at 45 km per hour. How much time will it take to cover the same distance at a speed of 30 km per hour?