Question

The distance between Delhi and Agra is 200 km. A train travels the first 100 km at a speed of 50 km/h. How fast must of the train travel the next 100 km, so as to average 70 km/h for the whole journey ?

Answer 1

Train must travel with 90 km/h so that its average speed remains 70 km/h

Explanation:

• Average speed of any journey is defined as total distance covered throughout the journey per unit total time taken during the journey, but if the whole journey is divided in two parts the we take the average speed as the sum of speeds and divide by 2 so in the given case we can use the latter concept as train covers the one half distance with some velocity and another half with different velocity

Given, distance between Delhi and Agra =  200 km

First 100 km at a speed = 50 km/h

Let next 100 km is moved at a speed of 's' km/h

Average speed 70 km/h is to be  maintained

Average speed = $\frac{sum of speeds}{2}$

=> 70 = $\frac{50+s}{2}$

=> 140 = 50 + s

=> s = 90 km/h

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