Samples of spring water were taken from two sources, presumably from the same spring. On
the basis of 6 analyses, the mean sodium content of the first sample is 3.92 ppm. Eight analyses of
a second sample gave a mean of 3.52 ppm sodium. The pooled analyses yielded a pooled standard
deviation of s = 0.20 ppm. Do the data indicate a difference between the sources of water at the
99% confidence level?

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