Chapter 8: Q 8.68. (page 331)

In each of Exercises $8.63 - 8.68$ , we provide a sample mean, sample size, population standard deviation, and confidence level In each case, perform the following tasks:
a. Use the one-mean $z -$ interval procedure to find a confidence interval for the mean of the population from which the sample was drawn.
b. Obtain the margin of error by taking half the length of the confidence interval.
c. Obtain the margin of error by using Formula $8 . l$ on page $325$
$x = 55, n = 16, σ = 5$ , confidence level $= 99 %$

Short Answer

Expert verified

Part (a) The $90 %$ confidence interval for $μ$ is $(51.7812, 58.2188)$

Part (b) The margin of error by using the half-length of the confidence interval is $3.2188$

Part (c) The margin of error by using the formula is $3.2188$

Step by step solution

Part (a) Step 1: Given information

$x = 55, n = 16, σ = 5$ , confidence level $= 99 %$

Part (a) Step 2: Concept

The formula used: the confidence interval $\bar{x} \pm z_{\frac{α}{2}} (\frac{σ}{\sqrt{n}})$ and $Margin of error (E) = z_{\frac{a}{2}} (\frac{σ}{\sqrt{n}})$

Part (a) Step 3: Calculation

Compute the $90 %$ confidence interval for $μ$

Consider $\bar{x} = 55, n = 16, σ = 5$ , and confidence level is $90 %$

The needed value of $z_{\frac{a}{2}}$ with a $90 %$ confidence level is $2.575$ , as shown in "Table II Areas under the standard normal curve."

Thus, the confidence interval is,

\bar{x} \pm z_{\frac{α}{2}} (\frac{σ}{\sqrt{n}}) = 55 \pm 2.575 (\frac{5}{\sqrt{16}}) = 55 \pm 2.575 (1.25) = 55 \pm 3.2188 = (51.7812, 58.2188)

Therefore, the $99 %$ confidence interval for $μ$ is $(51.7812, 58.2188)$

Part (b) Step 1: Calculation

Using the half-length of the confidence interval, calculate the margin of error.

Margin of error = \frac{58.2188 - 51.7812}{2} = \frac{6.4376}{2} = 3.2188

Thus, the margin of error by using the half-length of the confidence interval is $3.2188$

Part (c) Step 1: Calculation

Using a formula, calculate the margin of error.

Margin of error (E) = z_{\frac{a}{2}} (\frac{σ}{\sqrt{n}}) = 2.575 (\frac{5}{\sqrt{16}}) = 2.575 (1.25) = 3.2188

The margin of error by using the formula is $3.2188$

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Short Answer

Step by step solution

Part (a) Step 1: Given information

Part (a) Step 2: Concept

Part (a) Step 3: Calculation

Part (b) Step 1: Calculation

Part (c) Step 1: Calculation

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