Problem 69E

Assessing the bending strength of a wooden roof. Refer to the Journal of the International Association for Shell and Spatial Structures (Aug. 2004) study to estimate the mean bending strength of imported white wood used on the roof of an ancient Japanese temple, Exercise 6.31 (p. 318). Suppose you want to estimate the true mean breaking strength of the white wood to within 4 MPa using a 90% confidence interval. How many pieces of the imported wood need to be tested? Recall that the sample standard deviation of the breaking strengths from the study was 10.9 MPa.

Solution

Step 1 of 1

We have to find how many imported wood pieces need to be tested

From the given problem

From the the tables the critical value

The given error is e=4 MPa

And given standard deviation

The the sample size

=20.0920

Hence 20 imported wood pieces need to be tested