李太太开车从 P 镇出发前往 Q 镇，平均速度为 60 km/h。20 分钟后，库马尔先生开车从 Q 镇出发前往 P 镇，平均速度为 80 km/h。李太太在离开 P 镇 50 分钟后与库马尔先生相遇。P 镇和 Q 镇之间的距离是多少？ 答：___ km

1. Calculate the time Mrs Lee travelled

Mrs Lee travelled for $50$ minutes.
Time in hours = $\frac{50}{60} = \frac{5}{6}$ h.

2. Calculate the distance Mrs Lee travelled

Distance = Speed $\times$ Time
Distance = $60 \times \frac{5}{6} = 50$ km.

3. Calculate the time Mr Kumar travelled

Mr Kumar left $20$ minutes after Mrs Lee.
Time Mr Kumar travelled = $50 - 20 = 30$ minutes.
Time in hours = $\frac{30}{60} = \frac{1}{2}$ h.

4. Calculate the distance Mr Kumar travelled

Distance = Speed $\times$ Time
Distance = $80 \times \frac{1}{2} = 40$ km.

5. Calculate the total distance between Town P and Town Q

Total distance = Distance Mrs Lee travelled + Distance Mr Kumar travelled
Total distance = $50 + 40 = 90$ km.