A train covers a distance of 850 metres in 45 seconds. Travelling at the same speed, how many kilometres will the train cover in an hour?

The correct answer is 68 km.

We are given that a train covers 850 metres in 45 seconds, and we need to find how many kilometres it covers in 1 hour.

Step 1: Find the speed in metres per second (m/s)

\text{Speed}=\frac{850\text{m}}{45\text{s}}

Step 2: Convert speed from m/s to km/h

To convert metres per second to kilometres per hour, we multiply by the conversion factor 3600 / 1000 = 3.6, because there are 3600 seconds in an hour and 1000 metres in a kilometre.

\text{Speed (km/h)}=\frac{850}{45}\times 3.6

Step 3: Simplify the calculation

=\frac{850\times 3.6}{45}=\frac{3060}{45}=68\text{km/h}

Step 4: Interpret the result

Since the speed is 68 km/h, this means that in 1 hour, the train covers exactly 68 kilometres.

Therefore, the correct answer is Option 3: 68.