At 9 a.m., Riordan started from City X and travelled towards City Y and his speed remained constant throughout. At 10 a.m., Nicole started her journey from City X towards City Y at an average speed of 80 km/h. Nicole overtook Riordan at 1 p.m. After overtaking, Nicole carried on her journey at the same average speed and reached at City Y at 4:30 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 1 p.m. = 3 h

Distance that Nicole had travelled until Nicole overtook Riordan
= 3 x 80
= 240 km

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

Riordan's average speed
= 240 ÷ 4
= 60 km/h

(b)
From 10 a.m. to 4:30 p.m. = 6 h 30 min

1 h = 60 min
6 h 30 min = 6 ³⁰ ₆₀
 h = 6 ¹₂ h

Distance between the two cities
= 6 ¹₂ x 80
= ¹³₂ x 80
= 520 km

Answer(s): (a) 60 km/h; (b) 520 km