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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Originally Posted by matty888

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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Draw a Karnaugh table:



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.