The confidence interval given in Exercise 2 is based on df = 39, which is the “smaller of n1 — 1 and n2 — 1.” Use Formula 9-1 to find the number of degrees of freedom. Using the number of degrees of freedom from Formula 9-1 results in this confidence interval: 11.65 cm < µ1< µ2< 17.28 cm. In what sense is “df = smaller of n1 — 1 and n2 — 1” a more conservative estimate of the number of degrees of freedom than the estimate obtained with Formula 9-1?
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