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 05-10-2011, 06:41 PM #46 Senior Member   Join Date: May 2009 Location: South Florida Posts: 1,412 margin of error = z*sqrt(S^2/n) margin^2 = z^2*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. Reply
 05-10-2011, 06:45 PM #47 Junior Member   Join Date: Nov 2010 Posts: 77 Hey keasby where is the answer key to that test? Reply
 05-10-2011, 06:45 PM #48 Junior Member   Join Date: Dec 2010 Posts: 200 Here's a cram sheet: Statistics Study Sheet Here are calculator functions: http://www.pagesf.com/gal/stats/prep...ator_sheet.pdf Here are assumptions: http://apcentral.collegeboard.com/ap...tion_31840.pdf 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 Reply
 05-10-2011, 07:32 PM #49 Junior Member   Join Date: Dec 2010 Posts: 116 Can someone explain numbers 3,4,17,27,38 on the 2007 Test? Thanks Powered by Google Docs Reply
 05-10-2011, 07:56 PM #50 Junior Member   Join Date: Aug 2010 Posts: 299 #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*(standard deviation) greater than the mean. which is .3*.44=.132 greater than the mean. #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. #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? # 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. Last edited by AstroBlue; 05-10-2011 at 08:07 PM. Reply
 05-10-2011, 08:06 PM #51 Junior Member   Join Date: Apr 2011 Location: South Dakota --> Michigan '16 Posts: 91 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) 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) 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). I'll post the others, if they haven't been posted already, after I finish the test. Reply
 05-10-2011, 08:12 PM #52 Junior Member   Join Date: Apr 2011 Location: South Dakota --> Michigan '16 Posts: 91 @Astroblue On 17, the answers are referencing the statistic calculated not the p-value. Reply
 05-10-2011, 08:14 PM #53 Junior Member   Join Date: Aug 2010 Posts: 299 oh, okay, thanks for clearing that up Reply
 05-10-2011, 08:26 PM #54 Junior Member   Join Date: Apr 2011 Location: South Dakota --> Michigan '16 Posts: 91 Here's further explanation on 38: 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(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 Therefore (E). Reply
 05-10-2011, 08:30 PM #55 Junior Member   Join Date: Apr 2011 Location: South Dakota --> Michigan '16 Posts: 91 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). I don't know if this is the right way to go about this problem though. Reply
 05-10-2011, 09:07 PM #56 Junior Member   Join Date: Apr 2011 Posts: 40 Hey, can someone explain 6e of the 2010 stats test? (not form b) Thanks! Reply
 05-10-2011, 09:13 PM #57 Junior Member   Join Date: Apr 2011 Location: South Dakota --> Michigan '16 Posts: 91 @sarahchu http://apcentral.collegeboard.com/ap...guidelines.pdf The answer on page 18 seems to explain well enough. Reply
 05-10-2011, 09:17 PM #58 Junior Member   Join Date: Apr 2011 Posts: 40 Okay, thanks. I read the answer wrong and got confused >< Reply
 05-10-2011, 09:55 PM #59 Junior Member   Join Date: Apr 2010 Posts: 123 do they give us something besides the formula sheet? like a random number table, t distribution values, and standard normal probabilites? Reply
 05-10-2011, 10:02 PM #60 Junior Member   Join Date: Jul 2010 Posts: 92 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. Reply

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