John drives a car from city A to town B and then from town B to village C. He drives from city A to town B at a speed v km/h for t hours. It is known that the distance from town B to village C is 30% longer than that of from city A to town B. What is the percentage change of the car speed if he wants to reach the village C in a time 20% less than t hours?
answer: +62.5%
I don't know how to do!!!!!!!!
唔識做功課15
2013-09-27 6:56 am
回答 (1)
2013-09-27 2:14 pm
✔ 最佳答案
Distance from A to B = speed x time = vt km.So distance from B to C = vt(1 + 30%) = 1.3vt km.
Time to go from B to C = t(1 - 20%) = 0.8t hr.
So speed to go from B to C = distance/time = (1.3vt)/(0.8t) = (1.3/0.8)v km/hr
So % change in speed = (new speed - original speed)/original speed x 100%
= [(1.3v/0.8) - v]/v x 100%
= (1.3 - 0.8)/0.8 x 100%
= 0.5/0.8 x 100%
= 500/8 % = + 62.5%
收錄日期: 2021-04-13 19:44:27
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20130926000051KK00259