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Q.1.1

Expert-verifiedFound in: Page 501

Book edition
4th

Author(s)
David Moore,Daren Starnes,Dan Yates

Pages
809 pages

ISBN
9781319113339

To assess the accuracy of a laboratory scale, a standard weight known to weigh $10$ grams is weighed repeatedly. The scale readings are Normally distributed with unknown mean (this mean is $10$ grams if the scale has no bias). In previous studies, the standard deviation of the scale readings has been about $0.0002$ gram. How many measurements must be averaged to get a margin of error of $0.0001$ with $98\%$ confidence? Show your work.

The required number is $22$ .

Given in the question that, To assess the accuracy of a laboratory scale, a standard weight known to weigh $10$ grams is weighed repeatedly. The scale readings are Normally distributed with unknown mean (this mean is$10$ grams if the scale has no bias). In previous studies, the standard deviation of the scale readings has been about $0.0002$ gram . We need to find that how many measurements must be averaged to get a margin of error of $0.0001$ with $98\%$ confidence.

Population standard deviation $\left(\sigma \right)=0.0002$

Margin of error $\left(E\right)=0.0001$

Confidence level $=98\%$

The formula to compute the sample size is:

$n={\left(\frac{{z}_{\alpha /2}\times \sigma}{E}\right)}^{2}$

The z-score at $99\%$confidence level is calculated from the standard normal table like this,

${z}_{a/2}={z}_{0.02/2}$

$=2.33$

The number of measurements is calculated as:

$n={\left(\frac{{z}_{\alpha /2}\times \sigma}{E}\right)}^{2}$

$={\left(\frac{2.33\times 0.0002}{0.0001}\right)}^{2}$

$=21.648$

$\approx 22$

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