Question

An express train makes a run of 240 km at a certain speed. another train whose speed is 12km/hr less takes an hour longer to cover the distance. Find the speed of the express train in km/hr.

Answer 1

Solution:

Given:

Total distance = 240 km

Let the speed be x km/hr.

Therefore:

$\implies$ Time = 240/x hrs

$\implies$ New speed = x-12 km/hr

Now we know that,

$\implies$ Time = 240/x-12 hrs

Therefore:

$\implies$ 240/x-12 - 240/x = 1

$\implies$ 240x -240x + 2880/x^2-12x = 1

$\implies$ 2880 = x^2 - 12x

$\implies$ x^2 - 12x - 2880 = 0

By completing the squares, we get:

x = 60 or x = -48

Hence:

We know that, speed is non negetive, so -48 is discarded. Therefore, original speed of the express train is 60 km/hr.

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Answered by: Niki Swar, Goa❤️