Question

The respective ratio between the speeds of a car, a train and a bus is 5 : 9 : 4. The average speed of the car, the bus and the train is 72 km/h together. What is the average speed of the car and the train together ?
(1) 82 km/h (2) 78 km/h
(3) 84 km/h (4) Cannot be determined
(5) None of these

Answer 1

Let the speeds of the car, train and bus be 5x, 9x and 4x km/hr respectively.
Average speed = 5x + 9x + 4x/3 = 18x /3 = 6x km/hr.
Also, 6x = 72 => x = 12 km/hr
Therefore, the average speed of the car and train together is = 5x+9x/2= 7x = 7 x 12 = 84 km/hr.