Many ancient tombs were cut from limestone rock that contained uranium. Since most such tombs are not well-ventilated, they may contain radon gas. In one study, the radon levels in a sample of 12 tombs in a particular region were measured in becquerels per cubic meter

The question is incomplete. The complete question is :

Many ancient tombs were cut from limestone rock that contained uranium. Since most such tombs are not well-ventilated, they may contain radon gas. In one study, the radon levels in a sample of 12 tombs in a particular region were measured in becquerels per cubic meter . For this data, assume that and . Use this information to estimate, with 95% confidence, the mean level of radon exposure in tombs in the region. Interpret the resulting interval.

Solution :

Here, given

Mean sample,

Mean standard deviation , .

Sample size, n = 12

∴ Degree of freedom = n-1 = 12-1

                                            = 11

Significance level, α = 0.05

The critical level,

Therefore, lower limit =

                                   = 2951

Upper Limit  =

                                   = 4551

Therefore the confidence interval is with 95 % and the true mean level of radon exposure in the tombs is between  2951 and 4551 .