At 9 a.m., Justin started from City M and travelled towards City N and his speed remained constant throughout. At 10 a.m., Gem started her journey from City M towards City N at an average speed of 72 km/h. Gem overtook Justin at 3 p.m. After overtaking, Gem carried on her journey at the same average speed and reached at City N at 4:50 p.m.

1. Find Justin'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 Gem had travelled until Gem overtook Justin
= 5 x 72
= 360 km

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

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

(b)
From 10 a.m. to 4:50 p.m. = 6 h 50 min

1 h = 60 min
6 h 50 min = 6 ⁵⁰ ₆₀
 h = 6 ⁵₆ h

Distance between the two cities
= 6 ⁵₆ x 72
= ⁴¹₆ x 72
= 492 km

Answer(s): (a) 60 km/h; (b) 492 km