An article in Radio Engineering and Electronic Physics (1984, Vol. 29, No. 3, pp. 63–66) investigated the behavior of a stochastic generator in the presence of external noise. The number of periods was measured in a sample of 100 trains for each of two different levels of noise voltage, 100 and 150 mV. For 100 mV, the mean number of periods in a train was 7.9 with . For 150 mV, the mean was 6.9 with

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(a) It was originally suspected that raising noise voltage would reduce mean number of periods. Do the data support this claim? Use and assume that each population is normally distributed and the two population variances are equal. What is the P-value for this test?

(b) Calculate a confidence interval to answer the question in part (a).