A sample of 153 specimens was used in a tensile strength exp

A sample of 153 specimens was used in a tensile strength experiment (ksi). The mean tensile strength of the sample is 135.39 ksi, the standard deviation is 4.59 ksi, and the standard error of the mean is 0.37. We are 99% confident that the true average ultimate tensile strength is greater greater than ____________.

Solution

For 99% confidence on the right tail, using a z table,

z = 2.326347874

Thus, the standard error E is

E = z s / sqrt(n) = 0.863260021

Thus, the upper bound is

upper bound = Xbar + E = 135.39 + 0.863260021

upper bound = 136.25 [ANSWER]