Environmental Protection Agency standards require that the amount of lead in drinking water be less than 15 micrograms per liter. Twelve samples of water from a particular source have the following concentrations, in units of micrograms per liter:

a. Explain why it is necessary to check that the population is approximately normal before performing a hypothesis test.

b. Following is a dotplot of the data. Is it reasonable to assume that the population is approximately normal?

c. Assume that the population standard deviation is σ = 3.

If appropriate, perform a hypothesis test at the σ = 0.01 level to determine whether you can conclude that the mean concentration of lead meets the EPA standard. What do you conclude?

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