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20-hw8 - Stat 20 solutions to homework 8 Michael Lugo...

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Stat 20: solutions to homework 8 Michael Lugo November 8, 2010 1 Chapter 20, # 3 (a) 900 tickets – the number of tickets corresponds to the sample size. (b) a zero or a one, depending on whether the income is less than or greater than 50,000 dollars. (c) False; the SD of the box is 0 . 2 × 0 . 8 = 0 . 4. (d) True; the draws are the sample. (e) The number of high-income forms in the sample has EV . 2 × 900 = 180 and SE 900 × 0 . 4 = 12. We want to know the chance that between . 19 × 900 = 171 and . 21 × 900 = 189 forms are high-income. In standard units this is between - . 75 and . 75; the answer is 55%, from the normal table. (f) We can’t find this chance, because we don’t know the percentage of people with incomes over 75,000 dollars. (The normal curve can’t be used, since incomes are not normally distributed.) 2 Chapter 20, # 6 The answer is (ii). What matters is the absolute sample size, which is 35 , 000 for California and 2 , 000 for Nevada. 3 Chapter 20, # 11 (a) 357 , 340. (b) 71 . 4% , 68%. 4 Chapter 20, # 12 The total number of interviews is like the sum of 400 draws from a box with average 2 . 38 and SD 1 . 87. Therefore it has average 400
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