A 64 simple random sample of petrol consumption (litres per 100 kilometers. u) in private cars has been taken, yielding a mean consumption of 9.36 and a standard deviation of 1.4u. Then: Obtain a 96% confidence interval for the mean consumption. Assume both normality (for the consumption) and variance a = 2u2. How large must the sample be if, with the same confidence, we want the maximum error to be a quarter of litre?