For all of you who still need to complete your project...
If you were absent, you'll need to find a friend and steal some data. If you ask someone who was in class, they should have data combined from their group--just steal these numbers of "yes" and "no" for each of the three questions, add in your data, and work with this.
No one should be working with a data set of only 30 students...can you think of why?
For the rest of you, a few hints...
- Remember that your p-hat is not a number of "yes", like "23." P-hat is a proportion or percentage, so to get this you'll have to take the number of "yes" divided by the sample size.
- Use the correct z* value! Look in the chart! Remember, we're using three different levels of confidence--90% for the first question/interval, 95% for the second, 99% for the third.
- Use the Stat--Tests--One Prop Z-Int function on your calculator to actually find the interval; this is a good way to check your work. (You still need to show the formula written out with the correct numbers substituted (plugged) in.
- Use your book/Baron's review guide! Look for confidence intervals for proportions and you'll find examples with all the math/interpretations.