The 'reading age' of children about to start secondary school is a measure of how good they are at reading and understanding printed text. A child's reading age, measured in years, is denoted by the random variable X. The distribution of X is assumed to be Nu, o). The reading ages of a random sample of 20 children were measured, and the data obtained is summarised by Ex-232.6, Ex-2756.22.

(a) Calculate unbiased estimates of and o, giving your answers to correct to two decimal places.

(b) Calculate a symmetric 95% confidence interval for u. (C)