City C and City D were 324 km apart. A van travelled from City C towards City D. At the same time, a lorry started from City D to City C. After travelling 1²₅ h, the two vehicles were still 135 km apart. If the ratio of the average speed of the lorry to that of the van 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 1²₅ h by the two vehicles
= 324 - 135
= 189 km

Combined speed of the two vehicles
= 189 ÷ ⁷₅
= 189 x ⁵₇
= 135 km/h

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

4 u + 5 u = 9 u 
9 u = 135

1 u = 135 ÷ 9 = 15

Average speed of the lorry
= 4 u
= 4 x 15
= 60 km/h

(b)
Time taken for the lorry and the van to meet travelling the rest of the journey
= 135 ÷ 135
= 1 h 

Answer(s): (a) 60 km/h; (b) 1 h