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Caviar is an expensive delicacy, so companies that package it pay very close attention to the amount of product in their tins. Suppose a company that produces over 1,000 tins of caviar per day took a simple random sample (SRS) of 20 tins from one day's production. The sample showed a mean of 99.8 g of caviar per tin with a standard deviation of 0.9 g. The amounts were roughly symmetric with no outliers.

Based on this sample, which of the following is a [tex]95 \%[/tex] confidence interval for the mean amount of caviar (in grams) per tin from that day's production?

Choose 1 answer:

A. [tex]99.8 \pm 1.96\left(\frac{0.9}{\sqrt{20}}\right)[/tex]

B. [tex]99.8 \pm 2.093\left(\frac{0.9}{\sqrt{20}}\right)[/tex]

C. [tex]99.8 \pm 1.96 \sqrt{\frac{0.9(0.1)}{20}}[/tex]

D. [tex]99.8 \pm 1.96(0.9)[/tex]

E. [tex]99.8 \pm 2.093(0.9)[/tex]

Answer :

We are given a simple random sample (SRS) of 20 tins, with a sample mean of
[tex]$$\overline{x} = 99.8$$[/tex]
grams and a sample standard deviation of
[tex]$$s = 0.9$$[/tex]
grams. Since the sample size is small ([tex]$n=20$[/tex]) and the population standard deviation is unknown, we use the [tex]$t$[/tex]-distribution to construct a 95% confidence interval for the true mean amount of caviar per tin.

The steps are as follows:

1. Determine the Degrees of Freedom:
The degrees of freedom (df) is given by
[tex]$$\text{df} = n - 1 = 20 - 1 = 19.$$[/tex]

2. Find the Critical [tex]$t$[/tex] Value:
For a 95% confidence interval, we need the [tex]$t$[/tex]-value corresponding to a cumulative probability of [tex]$0.975$[/tex] (since 95% confidence level leaves 2.5% in each tail). For 19 degrees of freedom, this critical value is approximately
[tex]$$t^ \approx 2.093.$$[/tex]

3. Calculate the Standard Error (SE):
The standard error of the mean is
[tex]$$\text{SE} = \frac{s}{\sqrt{n}} = \frac{0.9}{\sqrt{20}}.$$[/tex]

4. Compute the Margin of Error (ME):
Multiply the critical [tex]$t$[/tex] value by the standard error:
[tex]$$\text{ME} = t^
\cdot \text{SE} = 2.093 \cdot \frac{0.9}{\sqrt{20}}.$$[/tex]

5. Form the Confidence Interval:
The 95% confidence interval for the mean is given by:
[tex]$$\overline{x} \pm \text{ME} = 99.8 \pm 2.093\left(\frac{0.9}{\sqrt{20}}\right).$$[/tex]

Thus, the correct answer is:

(B) [tex]$$99.8 \pm 2.093\left(\frac{0.9}{\sqrt{20}}\right).$$[/tex]

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Rewritten by : Jeany