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Chapter 8: Q.9 (page 523)

Good wood? A lab supply company sells pieces of Douglas fir 4inches long and 1.5inches square for force experiments in science classes. From experience, the strength of these pieces of wood follows a Normal distribution with standard deviation 3000pounds. You want to estimate the mean load needed to pull apart these pieces of wood to within 1000pounds with 95%confidence. How large a sample is needed? Show your work.

- Understand how the margin of error of a confidence interval changes with the sample size and the level of confidence C.

Short Answer

Expert verified

The sample size is35

Step by step solution

01

Step-1 Given Information

Given in the question that ,

Margin of error(E)=1000

Standard deviation蟽=3000

Confidence level=95%we have to find How large a sample is needed.

02

Step-2 Explanation

The value of z伪2corresponding to 95%confidence level 1.96which is obtained from standard normal table.

the sample size can be calculated as follows:

Samplesize(n)=z伪脳蟽2E2

=1.96脳300010002

鈮�35

Thus,the sample size is35

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