At 7 a.m., Billy started from City E and travelled towards City F and his speed remained constant throughout. At 9 a.m., Shiyun started her journey from City E towards City F at an average speed of 72 km/h. Shiyun overtook Billy at 1 p.m. After overtaking, Shiyun carried on her journey at the same average speed and reached at City F at 5:40 p.m.

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

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

Distance that Shiyun had travelled until Shiyun overtook Billy
= 4 x 72
= 288 km

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

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

(b)
From 9 a.m. to 5:40 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