A train runs first $75 \mathrm{~km}$ at a certain uniform speed and next $90 \mathrm{~km}$ at an average speed of $10 \mathrm{~km} / \mathrm{h}$ more than the normal speed. If it takes 3 hours to complete the journey, then how much time will the train take to cover $300 \mathrm{~km}$ with normal speed?

6 hours

Let train travels 75 km  with speed = S km/h

According to question ,

\(\frac{75}{S}\) + \(\frac{90}{S + 10}\) = 3

On solving ,

S = 50 km/h

So Time taken to cover 300 km with normal speed

= \(\frac{Distance}{Speed}\)

= \(\frac{300}{50}\)

= 6 hours