In Constructing a 99% Confidence Interval Estimate for the Difference

Multiple Choice

In constructing a 99% confidence interval estimate for the difference between the means of two normally distributed populations, where the unknown population variances are assumed not to be equal, summary statistics computed from two independent samples are as follows: $$\begin{array} { | l | l | l | } \hline n _ { 1 } = 28 & x - \operatorname { bar } _ { 1 } = 123 & s _ { 1 } = 8.5 \\\hline n _ { 2 } = 45 & x - \operatorname { bar } _ { 2 } = 105 & s _ { 2 } = 12.4 \\\hline\end{array}$$ The lower confidence limit is:

A) 24.485.
B) 11.515.
C) 13.116.
D) 22.884.