At 9 a.m., Bobby started from City M and travelled towards City N and his speed remained constant throughout. At 10 a.m., Sarah started her journey from City M towards City N at an average speed of 72 km/h. Sarah overtook Bobby at 3 p.m. After overtaking, Sarah carried on her journey at the same average speed and reached at City N at 1:20 p.m.

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

(a)
From 10 a.m. to 3 p.m. = 5 h

Distance that Sarah had travelled until Sarah overtook Bobby
= 5 x 72
= 360 km

From 9 a.m. to 3 p.m. = 6 h

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

(b)
From 10 a.m. to 1:20 p.m. = 3 h 20 min

1 h = 60 min
3 h 20 min = 3 ²⁰ ₆₀
 h = 3 ¹₃ h

Distance between the two cities
= 3 ¹₃ x 72
= ¹⁰₃ x 72
= 240 km

Answer(s): (a) 60 km/h; (b) 240 km