emiizladii
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- May 24, 2009
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A standard placement test has a mean of 115 and a standard deviation of ? = 10. Determine the minimum sample size if we want to be 95% certain that we are within 3 points of the true mean.
Statistics help please.
- Thread starter emiizladii
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This isn't anything fancy. Just use the formula \(\displaystyle n=\left(\frac{z\cdot {\sigma}}{E}\right)^{2}\)
Notice where this formula comes from?. It comes from the confidence interval formula solved for n:
\(\displaystyle E=z\cdot\frac{\sigma}{\sqrt{n}}\)
\(\displaystyle E\sqrt{n}=z{\sigma}\)
\(\displaystyle \sqrt{n}=\frac{z\sigma}{E}\)
\(\displaystyle n=\left(\frac{z\sigma}{E}\right)^{2}\)
Plug in your givens remembering that the z score for 95% is 1.96. Round up your solution.
Notice where this formula comes from?. It comes from the confidence interval formula solved for n:
\(\displaystyle E=z\cdot\frac{\sigma}{\sqrt{n}}\)
\(\displaystyle E\sqrt{n}=z{\sigma}\)
\(\displaystyle \sqrt{n}=\frac{z\sigma}{E}\)
\(\displaystyle n=\left(\frac{z\sigma}{E}\right)^{2}\)
Plug in your givens remembering that the z score for 95% is 1.96. Round up your solution.
D
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melius bd said:
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