HELP! URGENT!?
2017-08-28 10:41 pm
At 0900,a car left Town A and travelled towards Town B At an AVERAGE speed of 70km/h. At the same time, a lorry left Town B and travelled towards Town A at an AVERAGE speed of 55km/h. At 1100,the two vehicles were 35km apart. If the two vehicles had already passed each other before 1100,find the distance between the two towns.
回答 (3)
2017-08-28 11:11 pm
✔ 最佳答案
Let d km be the distance between Town A and Town B.Time taken = (11 - 9) hours = 2 hours
Total distance that the car and the lorry travel in km:
d + 35 = 70 × 2 + 55 × 2
d + 35 = 250
d = 215
Distance between Town A and Town B = 215 km
2017-08-28 10:59 pm
While the car and lorry are driving towards each other, the distance between them decreases by 70+55 = 125 km/h.
While the car and lorry are driving away from each other, the distance between them increases by 125 km/h.
They meet after x hours, x < 2. The car has traveled 70x km and the lorry has traveled 55x km.
After another 2-x hours, the car has traveled an additional (2-x)70 km and the lorry has traveled an additional (2-x)55 km.
(2-x)70 + (2-x)55 = 35
140-70x + 110-55x = 35
215 = 125x
x = 215/125 hours
The car and lorry met after 215/125 hours.
215/125 hours × (125 km)/hour = 215 km
The distance between towns is 215 km.
While the car and lorry are driving away from each other, the distance between them increases by 125 km/h.
They meet after x hours, x < 2. The car has traveled 70x km and the lorry has traveled 55x km.
After another 2-x hours, the car has traveled an additional (2-x)70 km and the lorry has traveled an additional (2-x)55 km.
(2-x)70 + (2-x)55 = 35
140-70x + 110-55x = 35
215 = 125x
x = 215/125 hours
The car and lorry met after 215/125 hours.
215/125 hours × (125 km)/hour = 215 km
The distance between towns is 215 km.
2017-08-28 10:55 pm
11 - 9 = 2 hrs.
2 * (70 + 55) = 250 km
250 - 35 = 215 km
2 * (70 + 55) = 250 km
250 - 35 = 215 km
收錄日期: 2021-04-18 17:45:35
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20170828144128AAjcxg5