Assume that the helium porosity (in percentage) of coal samplestaken from any particular seam is normally distributed with truestandard deviation 0.77.
(c) How large a sample size is necessary if the width of the 95%interval is to be 0.42? (Round your answer up to the nearest wholenumber.)
(d) What sample size is necessary to estimate true averageporosity to within 0.23 with 99% confidence? (Round your answer upto the nearest whole number.)
