Practice Final A WI 2011 SOLNS

X number preferring to work from home one day per

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X = number preferring to work from home one day per week X has a binomial distribution with n = 80 and p = .30 (n is too large for the table – need normal approximation) Check conditions for normal approximation: 1) np = 80x.3 = 24 is at least 10; and 2) n(1-p) = 80x.7 = 56 is at least 10. Use Z = (X – np)/(square root of np(1-p)) You want P(X at least 25) =P(Z at least (25-24)/square root (80x.3x.7) = =P(Z at least _________) = 1 – P(Z < ______) = ____________ This is an approximate answer. For #37: Bob measured the length (in cm) and weight (in grams) of a random sample of mice of a certain species. The results of his analysis are shown below. Variable Count Mean StDev Minimum Median Maximum Length 150 168.67 43.15 63.00 163.00 280.00 Weight 150 150.77 19.76 101.00 150.50 208.00 Predictor Coef SE Coef T P Constant 39.05 25.09 1.56 0.122 Weight 0.8597 0.1650 5.21 0.000 Pearson correlation of Length and Weight = 0.394 37. ESTIMATE the average weight of all mice of this species in the population. Show all work and use proper units WITH 95% CONFIDENCE. Best possible answer. Need a 95% confidence interval for average weight. Xbar plus/minus 1.96(standard deviation)/square root of n 7
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X = weight, n = 150, mean = 150.77, stdev = 19.76 Estimate is: 150.77 plus/minus 19.76/square root of 150 = 150.77 plus/minus ______________ GRAMS = ( , ) GRAMS 8
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