## 7.2 Concepts

Claire and Jake were wondering about the mean number of matches in a box. The boxes contain this statement:

An average of 45 matches per box.

They purchased a carton containing 25 boxes of matches,
and Jake counted the number of matches in *one* of those 25 boxes.
There was 44 matches.

'Oh wow. Just wow.' said Jake. 'They lie. There's only 44 in this box.'

What is Jake's misunderstanding?

Then, they counted the number of matches in

*each*of the twenty-five boxes.Claire found that the mean number of matches per box was 44.9 matches, and the standard deviation was \(0.124\).

Jake notes that the mean is 44.9 matches per box, and says: 'You can't have 0.9 of a match. That's dumb.' How would you respond?

'Wow!' said Jake. 'The claim is 45 matches per box on average, but the mean really is 44.9! They're liars! Liar, liar, pants on...'

What is Jake's misunderstanding?

What two broad reasons could explain why the sample mean is

*not*45?'Come on, Jake,' said Claire. 'As if the mean will be

*exactly*45 in a sample every single time. Let's work out the confidence interval.'Why does Claire think a CI is needed? What will it tell them?

What is an approximate 95% confidence interval for the mean for Claire's sample?

'Aha---I told you so! They

*are*absolutely lying! Your confidence interval doesn't even include their mean of \(45\)!' said Jake. 'The manufacturer*must*be lying!'Is Jake correct? Why or why not? What does the CI

*mean*?In this scenario, what does \(\bar{x}\) represent? What is the

*value*of \(\bar{x}\)?In this scenario, what does \(\mu\) represent? What is the

*value*of \(\mu\)?