City M and City N were 504 km apart. A sedan travelled from City M towards City N. At the same time, a lorry started from City N to City M. After travelling 1
12 h, the two vehicles were still 288 km apart. If the ratio of the average speed of the lorry to that of the sedan was 4 : 5, find
- the average speed of the lorry.
- the time taken for them to meet travelling the rest of the journey. Express your answer in h.
(a)
Distance covered in 1
12 h by the two vehicles
= 504 - 288
= 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 sedan = 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 sedan to meet travelling the rest of the journey
= 288 ÷ 144
= 2 h
Answer(s): (a) 64 km/h; (b) 2 h