A train moving with a speed 54 km/h crosses a platform and a man on the platform in 36 seconds and 20 seconds respectively. How long is the platform?

Let the length of train be l

             length of platform, p

speed of the train =$$ 54 km/hr \times \frac{5}{18} $$

                            = 15 m/s

train with a speed 15 m/s crosses a man on the platform in 20 seconds

therefore, $$ 15 m/s = \frac{l}{20} $$

solving we get l=300 m

train with a speed 15 m/s crosses a platform in 36 seconds

therefore, $$ 15 m/s = \frac{300+p}{36} $$

solving we get p=240 m