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Chapter 8: Q. R8.7 (page 548)

Good wood? A lab supply company sells pieces of Douglas fir 4 inches long and

1.5 inches square for force experiments in science classes. From experience, the strength of these pieces of wood follows a distribution with standard deviation 3000 pounds. You want to estimate the mean load needed to pull apart these pieces of wood to within 1000 pounds with 95% confidence. How large a sample is needed?

Short Answer

Expert verified

The required sample is35

Step by step solution

01

Given information

Standard deviation(蟽)=3000

Confidence level=95%

Margin of error(E)=1000

02

The objective is to find out the sample size to have the margin error within 1000pounds at 95%the confidence level.

We know,

The formula to compute the sample size is:

n=z伪2脳蟽E2

According to the standard normal table, the value of za2corresponding to the 95%confidence level is1.96

The sample size can be calculated as:

n=z伪2脳蟽E2=1.96脳300010002=34.5744鈮�35

Therefore, the sample size is35

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