2011 AP Statistics Thread

<p>ok thanks 10char</p>

<p><rant> So my teacher didn’t really teach us anything. He literally stood in front of the class everyday with a problem and said “well I didn’t really prepare for this, but I’ll see if I can muddle through it.” Then he’d get an answer and ask the class if it was right since we had answer printouts. He was wrong half the time. </rant></p>

<p>On another note, I’m on the stress bus through cram city right now. :P</p>

<p>If that AP Pass grade calculator is accurate then this test really should be no problem…</p>

<p>From the 2002 exam:</p>

<p>The lengths of individual shellfish in a population of 10,000 shellfish are approximately normally distributed with mean 10 centimeters and standard deviation 0.2 centimeter. Which of the following is the shortest interval that contains approximately 4,000 shellfish lengths?</p>

<p>(A) 0 cm to 9.949 cm
(B) 9.744 cm to 10 cm
(C) 9.744 cm to 10.256 cm
(D) 9.895 cm to 10.105 cm
(E) 9.9280 cm to 10.080 cm</p>

<p>The answer is D. Why is this? I don’t know how to solve this.</p>

<p>EDIT: Nevermind, I figured it out.</p>

<p>Can someone help me with conditional probability?</p>

<p>yea conditional probability is the probability of b given a and the formula is P(B|A)=P(AandB)/P(A); also, if P(B|A)=P(B) then A and B are independent</p>

<p>Can someone help me with binomialcdf(n,p,x)</p>

<p>Using the Barron’s example (9.21)
…If at least 8 of ten randomly picked articles meet all specifications, the whole shipment is approved. If, in reality, 85% of a particular shipment meet all specifications, what is the probability that the shipment will make it through the deck?</p>

<p>I don’t understand why it’s 1-binomcdf(10,.85,7) instead of 1-binomcdf(10,.85,8)</p>

<p>Ok thanks but the thing I don’t understand is the P(A and B)/P(B) because P(A and B) is P(A)*P(B). Wouldn’t the P(B) just cancel out every single time??? How is this not a self-defeating equation??</p>

<p>what are the different types of tests and when do you use them?
just need one sentence for each test plzzz</p>

<p>@momomomo: I think when they say P(A and B), it means both instances occurring at the same time while P(B) is when it’s only the probability of B occurring. </p>

<p>Here’s an example for you:
Suppose that, in a certain part of the world, in any 50-year period the probability of a major plague is .39, the probability of a major famine is .53, and the probability of both a plague and a famine is .15. What is the probability of a famine given that there is a plague?</p>

<p>P (both plague and famine)/ P(plague)= .15/.39= .385</p>

<p>I don’t know if that really helps. I think when you’re thinking of P(A and B), you refer to it as P(A) and P(B) when it’s really just given that there’s a probability being given for the intersection. Correct me if I’m wrong please.</p>

<p>Ohhh I think that is my mistake!! YAY thank you. So P(A and B) in the conditional prob equation isn’t a calculation, it’s just given?</p>

<p>Im pretty sure that the P(AandB) in the conditional probability formula means that the two are not independent. The formula for P(AandB) when they are both independent is P(A)*P(B). The practice problems that Ive done all had me reading from a table or they gave me the P(AandB) value…</p>

<p>Can someone help me with the binomcdf question and explain the differences between mutually exclusive and independence? </p>

<p>I think P(A and B) is usually given; it’d be awfully hard to calculate it, since my textbook and Barron’s don’t talk about calculations.</p>

<p>^ I need help with binomial and geometric distributions too</p>

<p>Is there going to be a lot about Type 1 and 2 errors and error probabilities/power of tests? my incompetent teacher skipped over this stuff…</p>

<p>my teacher told us not to worry about calculating power and Type II errors, but he said to know what each error was and be able to apply them in context</p>

<p>Okay thanks! That’s a relief.</p>

<p>@anotherindiankid: what troubles do you have with binomial and geometric?</p>

<p>I get the gist of it being that binomial distribution has a mean of np (sample size times population proportion), standard deviation as sqrt(np(1-p)), and the pdf measures the probability of an exact number of trials.</p>

<p>Geometric probability should be used for questions that ask for the first time a success should occur.</p>

<p>what’s the difference between p-hat and p? (sample proportions)</p>

<p>yea i understand the calculations, but i don’t know when to use which one. so, use geometric when they ask for the first time a success occurs? and when do you use binomials?</p>