City N and City P were 572 km apart. A sedan travelled from City N towards City P. At the same time, a lorry started from City P to City N. After travelling 1
23 h, the two vehicles were still 312 km apart. If the ratio of the average speed of the lorry to that of the sedan was 6 : 7, 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
23 h by the two vehicles
= 572 - 312
= 260 km
Combined speed of the two vehicles
= 260 ÷
53 = 260 x
35 = 156 km/h
Average speed of the lorry : Average speed of the sedan = 6 : 7
6 u + 7 u = 13 u
13 u = 156
1 u = 156 ÷ 13 = 12
Average speed of the lorry
= 6 u
= 6 x 12
= 72 km/h
(b)
Time taken for the lorry and the sedan to meet travelling the rest of the journey
= 312 ÷ 156
= 2 h
Answer(s): (a) 72 km/h; (b) 2 h