At 8 a.m., Riordan started from City Y and travelled towards City Z and his speed remained constant throughout. At 10 a.m., Kathy started her journey from City Y towards City Z at an average speed of 72 km/h. Kathy overtook Riordan at 2 p.m. After overtaking, Kathy carried on her journey at the same average speed and reached at City Z at 6:40 p.m.

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

(a)
From 10 a.m. to 2 p.m. = 4 h

Distance that Kathy had travelled until Kathy overtook Riordan
= 4 x 72
= 288 km

From 8 a.m. to 2 p.m. = 6 h

Riordan's average speed
= 288 ÷ 6
= 48 km/h

(b)
From 10 a.m. to 6:40 p.m. = 8 h 40 min

1 h = 60 min
8 h 40 min = 8 ⁴⁰ ₆₀
 h = 8 ²₃ h

Distance between the two cities
= 8 ²₃ x 72
= ²⁶₃ x 72
= 624 km

Answer(s): (a) 48 km/h; (b) 624 km