An article in Radio Engineering and Electronic Physics (1980, Vol. 25, pp. 74-79) 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 s1 = 2.6. For 150 mV, the mean was 6.9 with s_2 = 2.4. Use alpha = 0.01 and assume that each population is normally distributed and the two population variances are equal. (a) It was originally suspected that raising noise voltage would reduce mean number of periods. Do the data support this claim?
(b) Calculate a confidence interval to answer the question in part (a).