An article gave the following summary data on shear strength

An article gave the following summary data on shear strength (kip) for a sample of 3/8-in, anchor bolts: n = 63, bar X = 5.00, s = 1.20. Calculate a lower confidence bound using a confidence level of 90% for true average shear strength. (Round your answer to two decimal places.) kip

Solution

Given a=1-0.9=0.1, Z(0.1) = 1.28 (from standard normal table)

So the lower bound is

xbar -Z*s/vn =5-1.28*1.2/sqrt(63) = 4.81