Help me with AP Stats!

Test Preparation AP Test Preparation
1

<p>I need help with these corrections. I have the answer, I just need to know why they are the answers. Any help is greatly appreciated. </p>

<li>The number of undergraduates at John Hopkins University is approx 2,000, while the number at Ohio State University is approx 40,000. At both schools a simple random sample of about 3% of undergraduates is taken. Which of the following is the best conclusion?
a) The sample from John Hopkins has less sampling variability than that from Ohio State.
b) The sample from John Hopkins has more sampling variability than that from Ohio State.</li>
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<p>a - my answer
b- correct answer</p>

<p>2) It has been estimated that about 30% of frozen chickens contain enoguh salmonella bacteria to cause illness if improerly cooked. A consumer purchases 12 frozen chickens. What is the probability that the consumer will have more than 6 contaminated chickens?
d) 0.039</p>

<p>I know how to find it. You use 1 - binomialcdf(12,.3,6), but why do you subtract from one again? I know it has something to do with greater than and less than.</p>

<p>3) Suppose we select a SRS of size n = 100 from a large population having proportion p of successes. Let X be the number of successes in the sample. For which value of p would it be safe to assume the sampling distribution of X is approx normal?
b) 1/9
d) 0.9999</p>

<p>b - correct answer
d- my answer</p>

<p>4) If A U B = S (sample space), P(A and B compliment) = 0.25, and P(A compliment) = 0.35, then P (B) =
d) 0.75</p>

<p>didn’t answer this one, confused about it.</p>

<p>Use this for 19 and 20:
Erin averages $80 in tips on any given night as a server with a standard deviation of $12. Her friend Kyle averages $72 in tips on any given night with a standard deviation of $16. What is</p>

<p>I got 19 right but you need it to answer 20 so Ill post it.</p>

<p>19) If Erin and Kyle put their tips together, what can they expect to make together on any given night?
answer - $152</p>

<p>20) What is the standard deviation for problem number 19?
didn’t answer this one
answer- b) $20</p>

<p>i knew how to this, but i forget.</p>

2

<p>Please somebody!</p>

3

<p>John Hopkins has more sampling variability. As the sample size increases, the mean gets closer to the true mean. Ohio State has a much larger sample because the population is larger, and so the sample mean can be expected to be closer to the population mean. Think of it this way, you flip 3 heads, but you get 3 heads. Does that mean the probability of getting a head is 1.00? No, but as you keep flipping coins, say 100, you can expect the number of heads to regress to the mean, around 50.</p>

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<p>First of all, perhaps I should point out that on the great tree of math, statistics is the branch that got broken off by an overweight child sitting on it and turned into toothpicks for me to chew on. </p>

<p>Second of all, stats FTMFL (FTMFL=For the mutha-****in loss).</p>

<p>Third of all statistics reeks of phailure and is for liberal pencil pushers who can't even do math unless liberal english</p>

<p>Last of all, this thread phails and is now about nachos.</p>

5

<ol>
<li>The probability of getting 6 or less chickens is what you calculated (binomial(12,0.3,6)) and so 1- that is the probability that you get 7 or more chickens.</li>
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<p>lol u guys dont worry...i made a super review sheet (well it will be done by the weekend) for everything you need in stats...know everything there and you cant get lower than a 5 LOL!</p>

<p>BTW Heej is right...I love math, but statistics...makes my head spin in how pathetic of a course it is...easy curve + calculators throughout + not even a lot of math = O_O</p>

<p>Most math/science CCers should have no problem getting a perfect 5 on this...test, if you can call it that.</p>

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<p>Think about the first question in terms of numbers. If OSU has 20x the students of JH, then a 3% sample at OSU will have 20x the students than at JH. Larger sample size=>smaller sampling variability. OSU will have a much smaller sampling variability than JH.</p>

<p>For number 2: the binomialcdf(12, .3, 6) will give you the sum of the probabilities of having 0, 1, 2, 3, 4, 5, or 6 bad chickens out of 12. You want to know the probability of having more than 6, so you will want 1-bionomialcdf(12, .3, 6). That will give you the sum of the probabilities of having 7-12 bad chickens.</p>

<p>I have no idea what number 3 is trying to ask (is there missing info?), so I'll pass.</p>

<p>I can't seem to figure out number 4, but the concept isn't hard. Draw a simple Venn diagram with two overlapping circles. Since A U B=S, we only care about the circles and the overlapping region, aka P(complement(A U B))=0. Now name the left circle A and the right circle B. The leftmost area is region1, the overlap is region2, and the rightmost area is region3. If P(complement(A intersection B))=0.25, then region1+region3=0.25, and region2=0.75 (note: A intersection B is region2). P(complement(A))=0.35 indicates that region3=0.35 (because circle A is both region 1 and region2). Now you have a few equations and you should be able to solve for B (which is simply region2 + region3). If you try, however, you get that B=1.1, which is clearly wrong. Maybe you typed the problem wrong (hopefully)?</p>

<p>Twenty is not too bad at all. Say we have mean1 and std1, and mean2 and std2. Here, mean1=80, std1=12, mean2=72, and std2=16. Nineteen asks for the sum of the means, and mean1+mean2=152. Twenty asks for the new standard deviation. This isn't simple addition. Instead, the formula is: new std=sqrt(std1^2+std2^2). So new std=sqrt(144+256)=20.</p>

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<p>edit........</p>

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<p>3 confuses me, too. nope there was no other info. thats exactly what the question says.
i typed number 4 just as it is, too.</p>

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<p>WOW i can actually help someone on this website.</p>

<ol>
<li><p>one of the conditions for a proportion test is normality, which is implied when np > 10 and n(1-p) > 10.
D doesnt satisfy this because 100(0.001) < 10. b satisfies both; 100(1/9) >10 and 100(8/9) >10.</p></li>
<li><p>I'm assuming that by A and B complement you mean A and (B') not (A and B)'. becuase then it wouldn't make sense. other than that. if you use a venn diagram. A and B complement = 0.25 implies that ONLY A is 0.25. A' = 0.35 implies that ONLY B is 0.35. and since A U B = sample space, the middle area is equal to 0.4. Therefore, the P(B) = ONLY B + A and B = 0.35 + 0.4 = 0.75.</p></li>
<li><p>By definition, to calculate the standard deviation of a combination of data sets, you need to compare the variance (standard deviation squared). So the standard deviation of the combination is equal to the squareroot of (12^2 + 16^) = 20.</p></li>
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