Multiplication of Probabilities Problems

2008-05-24 2:31 am

1. Ken lives in Tuen Mun. He travels to school either by MTR or on foot. The probability of being late for school is 1/7 if he travels by MTR and 1/10 if he travels on foot.
a. Ken travels to school on foot on Monday, Tuesday and Wednesday. Find the probability that
(i) he will be late on Mon and Tue only in these three says;
(ii) he will be late on any two of these three days.

b. On Thursday, Ken goes to school to take part in a football match. If he is equally likely to travel by MTR or on foot, find the probability that he will be late on that day.

THX! =]

更新1:

What is 3C2 ?

回答 (3)

Audrey Hepburn

2008-05-24 2:37 am

✔ 最佳答案

a.i. P(late on Mon and Tues only on foot)
= P(Mon late) X P(Tues late) X P(Weds not late)
= 1/10 X 1/10 X (1 – 1/10)
= 9/1000

ii. P(late on any two days out of 3)
= 3C2X 9/1000
= 27/1000

b. P(late)
= P(MTR and late) P(on foot and late)
= 1/2 X 1/10 + 1/2 X1/7
= 17/140

2008-05-24 09:50:23 補充：
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Gabriella Montez

2008-05-24 9:42 pm

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cherk hong

2008-05-24 3:51 am

參考: a.i. P(late on Mon and Tues only on foot)

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