You Measure the Lifetime of a Random Sample of 25

Multiple Choice

You measure the lifetime of a random sample of 25 rats that are exposed to 10 Sv of radiation (the equivalent of 1000 REM) , for which the LD₁₀₀ is 14 days. The sample mean is x̄= 13.8 days. Suppose that the lifetimes for this level of exposure follow a Normal distribution, with unknown mean μ and standard deviation σ= 0.75 day. You read a report that says, "On the basis of a random sample of 25 rats, a confidence interval for the true mean survival time extends from 13.45 days to 14.15 days." What is the confidence level for this interval?

A) 90%
B) 95%
C) 98%
D) 99%