A machine fills bags of sugar and random sample of 20 bags selected from week's production yielded a mean weight of 499.1g with std deviation 0.63g. A wk later a sample of 25 bags yielded a mean weight of 500.2g with std deviation 0.48g. Test whether the mean during the second wk could be 500g. Use 5% significance level. Ans: t=2.041, reject Ho.