Suppose the porosity (in %) of coal samples taken from the (now closed) Prince M

Question

Suppose the porosity (in %) of coal samples taken from the (now closed) Prince Mine at Point Aconi, Nova Scotia was found to be normally distributed with -0.85 %. a.) Compute a 95 % confidence interval for the true mean porosity of Prince Mine coal if a sample of 25 specimens had an average porosity of 3.55 %. (Give decimal answer to two places past decimal.) Lower bound: 3.2200 Upper bound: 3.8800 160-96180 b) How large a sample size is necessary if the width of the 95 % CI is to be 0.35? (Give whole number answer.) 23 | . Tries 1/5 c.) what sample size is necessary to estimate the true mean porosity to within 0.25 (ie with half width 0.25) with 95% confidence? (Give whole number answer.) 178 . Tries 1/5

Explanation / Answer

b)
Upper limit - Lower limit = 2 ME
0.0035 = 2 ( z * (s/sqrt(n))
0.0035 = 2 *(1.96 *(0.0085/sqrt(n))
n = 91

c)

ME = 0.25
ME = z * (s/sqrt(n))
0.25 = 1.96 * ( 0.0085/sqrt(n))
n = 44

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