To determine how many minutes the train stops in an hour, let's break down the problem.

1. Given Speeds:

   • Without stoppages, the train travels at 72 km/hr.
   • With stoppages, the train's average speed reduces to 45 km/hr.

2. Difference in Distances Covered:

   • In one hour, the train should cover $72$ km if it doesn't stop.
   • However, with stoppages, it only covers $45$ km in one hour.

3. Lost Time Calculation:

   • The difference in distance covered is $72 - 45 = 27$ km.
   • This distance represents the time lost due to stoppages.

4. Time Lost in Minutes:

   • The speed without stoppages is 72 km/hr, so we calculate the time taken to cover 27 km: $\text{Time lost} = \frac{27 \text{ km}}{72 \text{ km/hr}} = \frac{3}{8} \text{ hours}$
   • Converting hours to minutes: $\frac{3}{8} \times 60 = 22.5 \text{ minutes}$

Therefore, the train stops for 22.5 minutes in an hour.

Would you like a further breakdown or have any questions?

---

Related Questions

1. What is the formula for calculating average speed?
2. If the train stopped for 30 minutes instead, what would its average speed be?
3. How much time would the train lose if its speed without stoppages was 90 km/hr instead of 72 km/hr?
4. How does increasing the train's speed without stoppages affect the average speed with stoppages?
5. If the stoppage time per hour varied, how would you determine the average speed?

Tip

In problems involving average speed and stoppages, always compare distances and use the difference to calculate lost time.