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 s = 2.6 For 150 mV, the mean was 6.9 with s = 2.4.

(a) It was originally suspected that raising noise voltage would reduce the mean number of periods. Do the data support this claim? Use α = 0.01 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).