Probability

[匿名]

2013-04-15 12:36 am

1. A bus will arrive at place A randomly between 3:00 and 3:30. I decide to go to
place A randomly between that time and wait for at most 5 minutes for the bus. If I
did not take a bus, I will take a train. What is the probabiliy that I will take a train?
Answer: 61/72
why I can't calculate as 1-(5/30) = 5/6

2. Two lines AB and CD with length 8 and 6 respectively. Two points P,Q were
chosen from these two lines respectively. Assume that I let PQ as the height of a
traingle, CQ as the base of a triangle. What is the probability that its area is greater
than 12.
Answer: (1-ln2)/2

更新1:

Sorry for number 2 the height of the triangle is AP

更新2:

點解知道3:00-3:25 同3:25-3:30 系吾同f(t)?點解要考慮2個case?

回答 (1)

用戶9112

2013-04-15 4:26 am

✔ 最佳答案

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圖片參考：http://imgcld.yimg.com/8/n/HA05107138/o/20130414202628.jpg

2013-04-15 20:29:33 補充：
When you reach A after 3:25, even though you wait there also for 5 minutes, but the bus will only arrive befoe 3:30. Let's say if you arrive at 3:27, there are only 3 minutes from 3:27 to 3:30 that the bus may come. For 2 of the minutes from 3:00 to 3:32 there bus will never come.

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