Question

Life tests performed on a sample of 13 batteries of a new model indicated: (1) an average life of 75 months, and (2) a standard deviation of 5 months. Other battery models, produced by similar processes, have normally distributed life spans. The 98% confidence interval for the population mean life of the new model is _________.
a) 63.37 to 86.63
b) 61.60 to 88.41
c) 71.77 to 78.23
d) 71.28 to 78.72
e) 79.86 to 81.28

Answer

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