Karen lives in Mong Kok and she can go to school either by bus or on foot. The probability of being late for school is 0.3 if she travels by bus, and is 0.1 if she travels on foot.
(a). Karen travels to school by bus on Wed, Thur and Friday in a certain week. Find the probability that she will be late on only one of these three days
(b). Karen goes to school to take part in an activity on Saturday. If she is equally likely to travel by bus or on foot, find the probability that she will not be late on that day.
the ans of (a) is 0.189 ;(b) 0.8
pls help me understand by showing the steps! thanks!!!
probability! pls help!!
2009-12-19 9:13 pm
回答 (2)
2009-12-19 9:26 pm
✔ 最佳答案
(a) The probability of being late in one day = 0.3The probability that she is not late in one day = 0.7
If she is late only for 1 day, there are 3C1 = 3 possibilities: late on Wed, late on Thur or late on friday.
Therefore the probability = 3 * 0.3 * 0.7^2 = 0.441
Your provided answer is for the case where she is late on 2 days.
(b) The probability that she is not late
= probability of taking bus and not late + probability of walking and not late
= (1/2)(1 - 0.3) + (1/2)(1 - 0.1)
= 0.35 + 0.45
= 0.8
2009-12-19 9:42 pm
(a)P(late on only one days)=P(late on Wed or late on Thur or late on Fri)
=P(late on Wed)+P(late on Thur)+P(late on Fri)
=0.3x0.7x0.7x3
=0.441
(b)P(late)=P[(travel by bus and late) or (on foot and late)]
=P(travel by bus and late)+P(on foot and late)
=1/2x0.3+1/2x0.1
=0.2
P(not be late)=1-P(late)
=1-0.2
=0.8
=P(late on Wed)+P(late on Thur)+P(late on Fri)
=0.3x0.7x0.7x3
=0.441
(b)P(late)=P[(travel by bus and late) or (on foot and late)]
=P(travel by bus and late)+P(on foot and late)
=1/2x0.3+1/2x0.1
=0.2
P(not be late)=1-P(late)
=1-0.2
=0.8
收錄日期: 2021-04-13 17:00:33
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