Environmental Science & Technology (Jan. 2005) reported a study of the reliability of a commercial kit to test for arsenic in groundwater. The field kit was used to test a sample of 328 groundwater wells in Bangladesh. If the color indicator on the field kit registers red, the the level of arsenic in the water is estimated to be at least 50 micrograms per liter: if the color registers green, the arsenic level is estimated to be below 50 micrograms pre liter. Use the information to find a 90% confidence interval for the true proportion of all groundwater wells in Bangladesh that have an estimated arsenic level below 50 micrograms per liter. Give a practical interpretation of the interval. Use data given in ASWELL.xls

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