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Math Help - Prob Qn'

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    Prob Qn'

    In testing the water supply for various cities for two kinds of impurities commonly found in water, it was found that 40% had an impurity of type A and 50% had an impurity of type B. 20% of the water supplies had neither sort of impurity (that is 20% did not have type A impurity and it did not have type B impurity). If a city is chosen at random, what is the probability that its water supply has exactly one type of impurity?
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    Quote Originally Posted by matty888 View Post
    In testing the water supply for various cities for two kinds of impurities commonly found in water, it was found that 40% had an impurity of type A and 50% had an impurity of type B. 20% of the water supplies had neither sort of impurity (that is 20% did not have type A impurity and it did not have type B impurity). If a city is chosen at random, what is the probability that its water supply has exactly one type of impurity?
    Draw a Karnaugh table:

    \, \begin{tabular}{l | c | c | c} & A & A$\, '$ & \\ \hline B & & & 0.5 \\ \hline B$\, '$ & & 0.2 & \\ \hline & 0.4 & & 1 \\ \end{tabular}

    I'm sure you can put in the missing probabilities.

    Use the table to get the values of Pr(A and B') and Pr(A' and B). Add these values together.

    For checking purposes: I get 0.3 + 0.4 = 0.7.
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