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13_exprmnt_dsgn2

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Midterm Exam 1

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Changing your grade given that grading is on a curve, the result would be Answers to the 10 (or so) most frequently missed questions #1 (a) 0.8% (b) 12.5% (c) 1.25% (d) 4% (e) 50% #1 • If you got this question right, The TA’s will not give you credit for a question that has an answer different from that in our answer key. • Why? Our answers are correct. If you were confused by some aspect of a question, chances are a bunch of other people were as well. We’d have to regrade everyone’s exams, to be fair, and little or no change to anyone’s grade. On planet gargu there are five different genders. A child can have only one of these genders. Picking a person at random, the probability of each of these genders is .2. Let’s say parents want to have three children in a row. What are the odds (before they have any children) that all three children will have the same gender? congratulations – you were one of the few in the class to get it right! Nonetheless, this is a simple probability problem, I expect you to be able to solve problems like this, and you should expected to be tested more on this on the final. 2
The catch E.G. One way of solving the problem – (0.2)(0.2)(0.2) = 0.008 Most people said the answer was (a) 0.8% However, this is the (correct) probability of having 3 children who all have a particular gender. it’s the probability of having 3 children who all have gender A The question doesn’t ask for that. It asks for the probability of having the 3 children have the same gender – this could be any of the 5 genders What is the probability of getting three kids all with a particular gender, e.g. A? Many people gave this answer, 0.8%. If you gave this answer, you didn’t take into account that this is just one possible gender, and you need to count all 5. (They are mutually exclusive events, so you can just add the probabilities.) Answer = (5)(0.008) = 0.04 = 4% Another way of solving the problem – AAA, BBB, CCC, DDD, EEE = 5 – 5·5·5 = 5 3 – 5/5 3 = 1/5 2 = 4/100 = 4% #2 book: Degrees of 25% 10% 5% 2.5% 1% 0.5% 9 0.70 1.38 1.83 2.26 2.82 3.25 10 0.70 1.37 1.81 2.23 2.76 3.17 11 0.70 1.36 1.80 2.20 2.72 3.11 obt How many possible ways can someone have 3 children of the same gender? Call the genders A, B, C, D, and E How many possible combinations of 3 children are there? What’s the probability of getting 3 kids all the same gender? The following lines appear in the t-table at the back of your freedom I calculate an observed value t of -2.24, from a sample of size 10. What do I conclude? 3

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Your choices 0 : µ = µ 0 a : µ µ 0 , and α =0.05. 0 : µ = µ 0 , with p<0.05, if a : µ µ 0 . only applies to the upper tail. (d) I accept the null hypothesis that µ < µ 0 . (e) I reject the null hypothesis, with p<0.025, if my a : µ µ 0 . Degrees of 25% 10% 5% 2.5% 1% 0.5% 9 0.70 1.38 1.83 2.26 2.82 3.25 10 0.70 1.37 1.81 2.23 2.76 3.17 11 0.70 1.36 1.80 2.20 2.72 3.11 t obt = -2.24, N=10 dealing with?
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