The mass, in grams, of a packet of biscuits of a particular brand, follows a normal distribution with mean u. Ten packets of biscuits are chosen at random and their masses noted. The results, in grams, are 397.3, 399.6, 401.0, 392.9, 396.8, 400.0, 397.6, 392.1, 400.8, 400.6 These can be summarised as follows: Ex-3978.8, Ex-1 583 098.3. Calculate a 95% confidence interval for u.