1Solid fuel is packed in sacks which are then weighed on scales. It is known that the weight of full sack is normally distributed with mean kg and standard deviation 0.36 kg. Four randomly selected sacks were weighted and the results were: 34.7, 34.4, 35.1 and 34.6 kg respectively.
(a)Calculate the 95% confidence interval for .
(b)State the sampling error of estimate with 95% confidence.
(c)How many full sacks have to be weighed so that there is 95% confidence that the error is within 0.15kg?
2. An online survey was conducted by the students union to estimate the proportion of college students with a mobile phone. Of the sample of 240 students surveyed, 185 had a mobile phone.
(a)Give a point estimate for the proportion in the population who have a
(b)Give the sampling error of estimate with 95% confidence.
(c)How large a sample must be taken to be 95% confident that the sample
proportion will be within 0.03 of the true proportion?