City V and City W were 648 km apart. A car travelled from City V towards City W. At the same time, a lorry started from City W to City V. After travelling 1¹₂ h, the two vehicles were still 432 km apart. If the ratio of the average speed of the lorry to that of the car was 4 : 5, find

1. the average speed of the lorry.
2. the time taken for them to meet travelling the rest of the journey. Express your answer in h.

(a)
Distance covered in 1¹₂ h by the two vehicles
= 648 - 432
= 216 km

Combined speed of the two vehicles
= 216 ÷ ³₂
= 216 x ²₃
= 144 km/h

Average speed of the lorry : Average speed of the car = 4 : 5

4 u + 5 u = 9 u 
9 u = 144

1 u = 144 ÷ 9 = 16

Average speed of the lorry
= 4 u
= 4 x 16
= 64 km/h

(b)
Time taken for the lorry and the car to meet travelling the rest of the journey
= 432 ÷ 144
= 3 h 

Answer(s): (a) 64 km/h; (b) 3 h