A measurement of fluoride ion in tooth paste from 5 replicate measurements delivers a mean of 0.14 % and a standard deviation of 0.05 %. What is the confidence interval at 95 % for which we assume that it contains the true value?

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Answer:

The confidence interval at 95 % for which we assume that it contains the true value is (0.0962, 0.1838).

Step-by-step explanation:

We have that to find our [tex]\alpha[/tex] level, that is the subtraction of 1 by the confidence interval divided by 2. So:

[tex]\alpha = \frac{1-0.95}{2} = 0.025[/tex]

Now, we have to find z in the Ztable as such z has a pvalue of [tex]1-\alpha[/tex].

So it is z with a pvalue of [tex]1-0.025 = 0.975[/tex], so [tex]z = 1.96[/tex]

Now, find M as such

[tex]M = z*\frac{\sigma}{\sqrt{n}}[/tex]

In which [tex]\sigma[/tex] is the standard deviation of the population and n is the size of the sample.

[tex]M = 1.96*\frac{0.05}{\sqrt{5}} = 0.0438[/tex]

The lower end of the interval is the mean subtracted by M. So it is 0.14 - 0.0438 = 0.0962

The upper end of the interval is the mean added to M. So it is 0.14 + 0.0438 = 0.1838

The confidence interval at 95 % for which we assume that it contains the true value is (0.0962, 0.1838).

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