# student3897

#### Probability

1. A fair dice is thrown twice. Find the probabilities that the sum of two numbers is greater than 9 given that at least one '6' is obtained.

Is the answer be 5/11 ? if not, can you teach me?

2. A fair dice is thrown twice. Find the probabilities that at least one '6' is obtained given that the sum of two numbers is greater than 9.

Is the answer be 5/6 ? if not, can you teach me?

3. John either takes train or a bus to school. He has a probability of 0.7 of taking train. The probabilities of being late if he takes train and a bus are 0.2 and 0.4 respectively. Find the probability that he is not late on a school day.

I can't think of the solution. Can you teach me??

Thank you !!

## 解答 0

• eric
2020-03-13 22:13:24
1. 5/36
• eric
2020-03-13 22:16:51
2. Yes
• eric
2020-03-13 22:19:01
0.7×0.8+0.3×0.6
• eric
2020-03-13 22:21:08
3.
•  eric 2020-03-13 22:19:01
• 0.7×0.8+0.3×0.6
• student3897
2020-03-13 23:00:23
可唔可以講解下步驟/列式？thank you !
•  eric 2020-03-13 22:13:24
• 1. 5/36
• student3897
2020-03-13 23:04:07
想問下點解係0.7×0.8同埋0.3×0.6？知道0.8, 0.6分別係prob. of not being late. 想知道點解係相乘。thank you !!
•  eric 2020-03-13 22:19:01
• 0.7×0.8+0.3×0.6
• eric
2020-03-14 09:26:17
因為P(A and B occur)=P(A)×P(B if A occurs)
• student3897
2020-03-14 09:35:20
thanks !
•  eric 2020-03-14 09:26:17
• 因為P(A and B occur)=P(A)×P(B if A occurs)
• student3897
2020-03-14 09:36:19
請問為何第一題是這個答案？謝謝!
•  eric 2020-03-13 22:13:24
• 1. 5/36
• eric
2020-03-14 10:18:04
5:(4,6),(6,4),(5,6),(6,5),(6,6) 36=6×6
• student3897
2020-03-14 11:51:14
我的理解是這樣，這樣對嗎？不明白為什麼分母會是36。謝謝！

#### 附加文件

•  eric 2020-03-14 10:18:04
• 5:(4,6),(6,4),(5,6),(6,5),(6,6) 36=6×6
• eric
2020-03-14 12:32:10
你做得啱，是我攪錯了，sorry!

jpg, gif, png, doc, docx, pdf, xls, mov, mp4, m4a, mp3 (檔案上限為50M)