Milk cartons are advertised to contain one litre of milk. From a randomly sample of 18 one-litre cartons whose contents were accurately measured by the South African Bureau of Standards (SABS). It was found that the average fill was 0.98 litres with a sample standard deviation of 0.052 litres. Assume that the fill of one litre milk cartons is normally distributed.

Using a 99% confidence level estimate the actual mean fill of all one litre milk cartons. Interpret your findings and comment on the question : ‘Do one litre cartons of milk cartons contain one litre of milk on average’?