Acidity of mouthwash. Acid has been found to be a primary cause of dental caries (cavities). It is theorized that oral mouthwashes contribute to the development of caries due to the antiseptic agent oxidizing into acid over time. This theory was tested in the Journal of Dentistry, Oral Medicine and Dental Education (Vol. 3, 2009). Three bottles of mouthwash, each of a different brand, were randomly selected from a drugstore. The pH level (where lower pH levels indicate higher acidity)

of each bottle was measured on the date of purchase and after 30 days. The data are shown in the next table. Conduct an analysis to determine if the mean initial pH level of mouthwash differs significantly from the mean pH level after 30 days. Use a = .05 as your level of significance.

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Mouthwash Brand Initial pH Final pH LMW 4.56 4.27 SMW 6.71 6.51 RMW 5.65 5.58