39. The following data summary was obtained from a comparison of the lead content of human hair removed from adult individuals that had died between 1880 and 1920 with the lead content of present-day adults. The data are in units of micrograms, equal to one-millionth of a gram.

(a) Do the above data establish, at the 1 percent level of significance, that the mean lead content of human hair is less today than it was in the years between 1880 and 1920? Clearly state what the null and alternative hypotheses are.

(b) What is the p-value for the hypothesis test in part (a)?

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1880-1920 Today Sample size: 30 100 Sample mean: 48.5 26.6 Sample standard deviation: 14.5 12.3