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Ludmilka [50]
3 years ago
9

In a random sample of 150 customers of a high-speed Internetprovider, 63 said that their service had been interrupted one ormore

times in the past month.A) Find a 95% confidence interval for the proportion of customerswhose service was interrupted one or more times in the pastmonth.B) Find a 99% confidence interval for the proportion of customerswhose service was interrupted one or more times in the pastmonth.C) Find the sample size needed for a 95% confidence interval tospecify the proportion to within -+ 0.05.D) Find the sample size needed for a 99% confidence interval tospecify the proportion to within -+ 0.05.
Mathematics
1 answer:
erastovalidia [21]3 years ago
5 0

Answer:

a) The 95% confidence interval would be given by (0.341;0.499)

b) The 99% confidence interval would be given by (0.316;0.524)

c) n=335

d)n=649

Step-by-step explanation:

1) Notation and definitions

X_{IS}=63 number of high speed internet users that had been interrupted one or more times in the past month.

n=150 random sample taken

\hat p_{IS}=\frac{63}{150}=0.42 estimated proportion of high speed internet users that had been interrupted one or more times in the past month.

p_{IS} true population proportion of high speed internet users that had been interrupted one or more times in the past month.

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

The population proportion have the following distribution

p \sim N(p,\sqrt{\frac{\hat p(1-\hat p)}{n}})

1) Part a

In order to find the critical value we need to take in count that we are finding the interval for a proportion, so on this case we need to use the z distribution. Since our interval is at 95% of confidence, our significance level would be given by \alpha=1-0.95=0.05 and \alpha/2 =0.025. And the critical value would be given by:

t_{\alpha/2}=-1.96, t_{1-\alpha/2}=1.96

The confidence interval for the mean is given by the following formula:

\hat p \pm z_{\alpha/2}\sqrt{\frac{\hat p (1-\hat p)}{n}}

If we replace the values obtained we got:

0.42 - 1.96\sqrt{\frac{0.42(1-0.42)}{150}}=0.341

0.42 + 1.96\sqrt{\frac{0.42(1-0.42)}{150}}=0.499

The 95% confidence interval would be given by (0.341;0.499)

2) Part b

In order to find the critical value we need to take in count that we are finding the interval for a proportion, so on this case we need to use the z distribution. Since our interval is at 99% of confidence, our significance level would be given by \alpha=1-0.99=0.01 and \alpha/2 =0.005. And the critical value would be given by:

t_{\alpha/2}=-2.58, t_{1-\alpha/2}=2.58

The confidence interval for the mean is given by the following formula:

\hat p \pm z_{\alpha/2}\sqrt{\frac{\hat p (1-\hat p)}{n}}

If we replace the values obtained we got:

0.42 - 2.58\sqrt{\frac{0.42(1-0.42)}{150}}=0.316

0.42 + 2.58\sqrt{\frac{0.42(1-0.42)}{150}}=0.524

The 99% confidence interval would be given by (0.316;0.524)

3) Part c

The margin of error for the proportion interval is given by this formula:

ME=z_{\alpha/2}\sqrt{\frac{\hat p (1-\hat p)}{n}}    (a)

And on this case we have that ME =\pm 0.05 and we are interested in order to find the value of n, if we solve n from equation (a) we got:

n=\frac{\hat p (1-\hat p)}{(\frac{ME}{z})^2}   (b)

And replacing into equation (b) the values from part a we got:

n=\frac{0.42(1-0.42)}{(\frac{0.05}{1.96})^2}=374.32

And rounded up we have that n=335

4) Part d

The margin of error for the proportion interval is given by this formula:

ME=z_{\alpha/2}\sqrt{\frac{\hat p (1-\hat p)}{n}}    (a)

And on this case we have that ME =\pm 0.05 and we are interested in order to find the value of n, if we solve n from equation (a) we got:

n=\frac{\hat p (1-\hat p)}{(\frac{ME}{z})^2}   (b)

And replacing into equation (b) the values from part a we got:

n=\frac{0.42(1-0.42)}{(\frac{0.05}{2.58})^2}=648.599

And rounded up we have that n=649

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