At 8 a.m., Mark started from City W and travelled towards City X and his speed remained constant throughout. At 9 a.m., Shiyun started her journey from City W towards City X at an average speed of 90 km/h. Shiyun overtook Mark at 1 p.m. After overtaking, Shiyun carried on her journey at the same average speed and reached at City X at 1:30 p.m.

1. Find Mark's average speed in km/h.
2. What is the distance between the two cities?

(a)
From 9 a.m. to 1 p.m. = 4 h

Distance that Shiyun had travelled until Shiyun overtook Mark
= 4 x 90
= 360 km

From 8 a.m. to 1 p.m. = 5 h

Mark's average speed
= 360 ÷ 5
= 72 km/h

(b)
From 9 a.m. to 1:30 p.m. = 4 h 30 min

1 h = 60 min
4 h 30 min = 4 ³⁰ ₆₀
 h = 4 ¹₂ h

Distance between the two cities
= 4 ¹₂ x 90
= ⁹₂ x 90
= 405 km

Answer(s): (a) 72 km/h; (b) 405 km