#20

To reduce laboratory costs, water samples from four public swimming pools are combined for one test for the presence of bacteria. Further testing is done only if the combined sample tests positive. Based on past results, there is a 0.004 probability of finding bacteria in a public swimming area. Find the probability that a combined sample from four public swimming areas will reveal the presence of bacteria. Is the probability low enough so that further testing of the individual samples is rarely necessary? The probability of a positive test result is (Round to three decimal places as needed.) prrect