The email usage for two different plants of a large company was compared at level of significance 0.05. A sample of 50 employees was selected at each plant. The mean number of email messages sent per employee for one plant was 15.5 per week and the standard deviation was 5.0. For the other plant, the mean was 18.4 and the standard deviation was 3.6. For the test of equal population means versus unequal population means, the absolute value for the computed test statistic, the critical values, and the p-value respectively are: Which one?
a) 2.33, + - 1.96, 0.0008
b) 3.33, + - 2.33, 0.0008
c) 3.33, + - 1.96, 0.0008
d) 2.33, + - 1.65, 0.0004
The difference of mean is
The standard error of the difference is ...
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