Question 754989: The probabilty that it is Monday and that a student is absent is 0.05. Since there are 5 days of school in a week, the probability that it is Monday is 0.2. What is the probability that a student is absent on Monday.
Answer by DrBeeee(684)   (Show Source):
You can put this solution on YOUR website! The Prob(Monday and Absent) = Prob(Monday)*Prob(Absent), or
(1) P(M and A) = P(M)*P(A) or
(2) P(M)*P(A) = P(M)*P(A) or
(3) P(M)*P(A) = 0.05
Since P(M) = 0.2 we have
(4) 0.2*P(A) = 0.5 or
(5) P(A) = 0.05/0.2 or
(6) P(A) = 0.25
Answer: The probability that a student is absent on a Monday is 0.25.
Comment: A more exact statement of the probability is usually given by,
(7) P(M and A) = P(M)*P(A/M), where P(A/M) is the conditional probability that being absent happens given that it is Monday. The answer for the stated problem is correct, however it may be different if it were on a Wednesday. Because we expect fewer absentees on Wdenesday than on Monday (or Friday). In these cases the conditional probability, P(absent/weekday) would differ depending on the day of the week.
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