At 7 a.m., Riordan started from City T and travelled towards City U and his speed remained constant throughout. At 8 a.m., Erika started her journey from City T towards City U at an average speed of 72 km/h. Erika overtook Riordan at 1 p.m. After overtaking, Erika carried on her journey at the same average speed and reached at City U at 6:45 p.m.

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

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

Distance that Erika had travelled until Erika overtook Riordan
= 5 x 72
= 360 km

From 7 a.m. to 1 p.m. = 6 h

Riordan's average speed
= 360 ÷ 6
= 60 km/h

(b)
From 8 a.m. to 6:45 p.m. = 10 h 45 min

1 h = 60 min
10 h 45 min = 10 ⁴⁵ ₆₀
 h = 10 ³₄ h

Distance between the two cities
= 10 ³₄ x 72
= ⁴³₄ x 72
= 774 km

Answer(s): (a) 60 km/h; (b) 774 km