document.write( "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. \n" ); document.write( "

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The Prob(Monday and Absent) = Prob(Monday)*Prob(Absent), or
\n" ); document.write( "(1) P(M and A) = P(M)*P(A) or
\n" ); document.write( "(2) P(M)*P(A) = P(M)*P(A) or
\n" ); document.write( "(3) P(M)*P(A) = 0.05
\n" ); document.write( "Since P(M) = 0.2 we have
\n" ); document.write( "(4) 0.2*P(A) = 0.5 or
\n" ); document.write( "(5) P(A) = 0.05/0.2 or
\n" ); document.write( "(6) P(A) = 0.25
\n" ); document.write( "Answer: The probability that a student is absent on a Monday is 0.25.
\n" ); document.write( "Comment: A more exact statement of the probability is usually given by,
\n" ); document.write( "(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. \n" ); document.write( "

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