<p>No way. That’s worded awfully. Well, thank you! I’ll be sure to remember this if it shows up tomorrow.</p>
<p>Can anyone help me with this?
A large company is considering opening a franchise in St . Louis and wants to
estimate the mean household income for the area using a simple random sample
of households . Based on information from a pilot study, the company assumes
that the standard deviation of household incomes is σ = $7,200 . Of the following,
which is the least number of households that should be surveyed to obtain
an estimate that is within $200 of the true mean household income with
95 percent confidence?
(a) 1,375
(b) 1,300
(c) 5,200
(d) 5,500
(e) 7,700</p>
<p>My class has done 5 practice exams (the ones from Barron’s - school buys them) and about 5 sets of previous free-response questions. Needless to say, I feel pretty prepared. Best stat teacher ever.</p>
<p>@AstroBlue - What’s the answer? I got C. Least would be 4978.7, but out of those choices the least would be 5,200.</p>
<p>the answer is c, it’s one of the sample questions from the AP Course Description, can you explain your method please?</p>
<p>margin of error = z<em>sqrt(S^2/n)
margin^2 = z^2</em>S^2/n
n = z^2*S^2/margin^2
n = 1.96^2 * 7200^2 / 200^2
n = 4978.7, rounds up to 4979 as the minimum sample size, so we take the next-highest answer choice, which is C.</p>
<p>Hey keasby where is the answer key to that test?</p>
<p>Here’s a cram sheet:
[Statistics</a> Study Sheet](<a href=“http://www.scribd.com/doc/93338/Statistics-Study-Sheet]Statistics”>http://www.scribd.com/doc/93338/Statistics-Study-Sheet)</p>
<p>Here are calculator functions:
<a href=“http://www.pagesf.com/gal/stats/prep/calculator_sheet.pdf[/url]”>http://www.pagesf.com/gal/stats/prep/calculator_sheet.pdf</a></p>
<p>Here are assumptions:
<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>And I also found this on the internet (I didn’t come up with this, some teacher named Mr. Dooley did; I just copied and pasted it):
Here is a good way to remember the assumptions/conditions for inference for the slope of the true LSRL.
L – The mean response μy has a straight Line relationship with x. μy=α+βx The slope β and intercept α are unknown parameters.
I – Repeated responses y are Independent of each other.
N – residuals have approximately Normal distribution
E – residuals have Equal variance</p>
<p>Can someone explain numbers 3,4,17,27,38 on the 2007 Test? Thanks
[Powered</a> by Google Docs](<a href=“http://docs.google.com/viewer?a=v&q=cache:u6pG3lWoKPYJ:guggswiki.wikispaces.com/file/view/2007%2BMC.pdf+the+distribution+of+the+diameters+of+a+particular+variety+of+oranges+is+approximately+normal&hl=en&gl=us&pid=bl&srcid=ADGEESiXz2FWcFXzed84JX7eWsDvkaHFyX8aob6ot05RKPHprZOlgAz_Dyao90ERi7dvGqyAQHSW_RgVAczjSxBJYzFSIx_UHOzwExrU0TpkH9HO8oIs8k3RC8zuiaj7g5EjGGa3AI8N&sig=AHIEtbQla72z4iCQNaAdeFKBD1uG6qVPfw]Powered”>http://docs.google.com/viewer?a=v&q=cache:u6pG3lWoKPYJ:guggswiki.wikispaces.com/file/view/2007%2BMC.pdf+the+distribution+of+the+diameters+of+a+particular+variety+of+oranges+is+approximately+normal&hl=en&gl=us&pid=bl&srcid=ADGEESiXz2FWcFXzed84JX7eWsDvkaHFyX8aob6ot05RKPHprZOlgAz_Dyao90ERi7dvGqyAQHSW_RgVAczjSxBJYzFSIx_UHOzwExrU0TpkH9HO8oIs8k3RC8zuiaj7g5EjGGa3AI8N&sig=AHIEtbQla72z4iCQNaAdeFKBD1uG6qVPfw)</p>
<h1>3. The 67th percentile means 67 percent of all values are below it, right? So essentially, we want to find the critical value that corresponds to a p-value of .67, which would be like invNorm(.67) on your calculator, which is .44, this means that for a value to be in the 67th percentile in a normal model, it must be .44<em>(standard deviation) greater than the mean. which is .3</em>.44=.132 greater than the mean.</h1>
<h1>4 To start off, find the critical value (z*) that corresponds to a confidence level of .9, which is 1.644, so we can cross off B and D. C and E dont look like any test that I know of, so cross that out. Leaving only A. If you want to actually do it, the test is a 2 proportion z interval, so you would look on your formula sheet for the standard deviation that corresponds to that CI.</h1>
<h1>7 This is a X2 GOF test I think. But dont worry about that part, you have the X2 value and the degrees of freedom (4-1 or 3), so plug those into your calculator and you get a p value of .045. The null hypothesis for X2 test would be that the observed results are the same as the predicted ones, because we have a p value thats less than our alpha level, we can reject the Ho. So B…but the answer key says A…what did I do wrong?</h1>
<h1>38 Common sense would lead you to D or E as the answer. Simply computing the probability for getting a 0 total gives E as the answer.</h1>
<p>3: invnorm(.67) will give you the z-score or the number of standard deviations above/below the mean depending on the sign.
(.4399)(.3)=.132
(C)</p>
<p>4: Interval = difference of proportions ± (critical value)(standard error/deviation)
Critical value = invNorm(.95)=1.645 eliminating (B) and (D).
Standard error/deviation follows the formula sheet
(A)</p>
<p>17: I just did a quick GOF test on my calculator and got a p-value of .045, so it’s significant, which means A or B. Chi-square tests are always one-sided (greater than) so it is (A).</p>
<p>I’ll post the others, if they haven’t been posted already, after I finish the test.</p>
<p>@Astroblue
On 17, the answers are referencing the statistic calculated not the p-value.</p>
<p>oh, okay, thanks for clearing that up :D</p>
<p>Here’s further explanation on 38:</p>
<p>For the first game you can get 0, 1, or 2. The same thing for the second. Adding all the possibilities gives 0 (0+0), 1 (0+1), 2 (1+1, 0+2), 3 (1+2), or 4 (2+2). This eliminates everything except for (D) and (E).</p>
<p>P(0) = (.3)(.3) = .09
P(1) = 2(.3)(.4) = .24
P(2) = (.4)(.4) + 2(.3)(.3) = .34
P(3) = 2(.4)(.3) = .24
P(4) = (.3)(.3) = .09</p>
<p>Therefore (E).</p>
<p>27: This one’s just confusing. I just did 1 - .056 and got .944. The widest confidence interval therefore that’s narrower than 94.4% would be 93% or (B).</p>
<p>I don’t know if this is the right way to go about this problem though.</p>
<p>Hey, can someone explain 6e of the 2010 stats test? (not form b)
Thanks!</p>
<p>@sarahchu
<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>The answer on page 18 seems to explain well enough.</p>
<p>Okay, thanks. I read the answer wrong and got confused ><</p>
<p>do they give us something besides the formula sheet? like a random number table, t distribution values, and standard normal probabilites?</p>
<p>They “just” give us the 7-page formula packet, and if there’s a simulation-type problem I think they’ll give us a list of random numbers to use if they don’t want us to use randInt.</p>