A random sample of medical files is used to estimate the proportion p of all peo

Question

A random sample of medical files is used to estimate the proportion p of all people who have blood type B. (a) If you have no preliminary estimate for p, how many medical files should you include in a random sample in order to be 85% sure that the point estimate p^hat will be within a distance of 0.04 from p? (Round your answer up to the nearest whole number.) ____ medical files (b) Answer part (a) If you use the preliminary estimate that about 11 out of 90 people have blood type B. _____ medical files

Explanation / Answer

5)

a)

margin of error = 0.04

z-score* std/sqrt(n) = 0.04

=>

1.44 * sqrt( 0.5 * 0.5/n) = 0.04

=>

size of sample n = 324

b)

p-estimate = 11/90

margin of error = 0.04

=>

1.44 * sqrt( 11/90 * 79/90 * 1/n) = 0.04

=>

n = 139

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