Question

In a study of 250 adults, the mean heart rate was 70 beats per minute. Assume the population of heart rates is known to be approximately normal with a standard deviation of 12 beats per minute. What is the 99% confidence interval for the mean beats per minute?

Answer 1

68.9 – 76.3

70 – 72

61.2 – 72.8

68 – 72

Answer 2

Is the ans 68-72??

Answer 3

I'm trying to find out for my self

Answer 4

The confidence interval will look like this:
\[\left(\bar{x}-Z_{\alpha/2}\frac{\sigma}{\sqrt n},~\bar{x}+Z_{\alpha/2}\frac{\sigma}{\sqrt n}\right)\]
where
\[\begin{align*}\bar{x}&:~\text{sample mean}\\
Z_{\alpha/2}&:~\text{critical value for a }(1-\alpha)\times100\%\text{ confidence level}\\
\sigma&:~\text{standard deviation}\\
n&:~\text{sample size}
\end{align*}\]
Can you identify what's what from the given information?

Answer 5

not at all

Answer 6

[70 - 2.575.12\div \sqrt{250} ,70+ 2.575.12\div \sqrt{250}\]

Answer 7

"In a study of 250 adults,...". So \(n=250\).

"... the mean heart rate was 70 bpm." So \(\bar{x}=70\).

"... with a standard deviation of 12 bpm." So \(\sigma=12\).

A 99% confidence level has a critical value of approximately \(Z_{\alpha/2}=2.576\).

Answer 8

so the answer is b?

Answer 9

B is th ans.