Jeff decides to streamline the food serving procedure so as to shorten the serving time of an order. Assume that the improved serving time of an order can be modelled by a normal distribution with mean I) seconds and standard deviation 10 seconds. Jeff selects a random sample of 77. orders and records their serving times. He then uses the sample mean as an estimate of I). (f) The number n is chosen such that the probability of the absolute difference between the estimated value and the true value being within 0.5 standard deviation is at least 0.9. (i) State the probability distribution followed by the sample mean. Express your answer in terms of b and n. [2 marks] (ii) Find the least value of n. [4 marks] (g) Suppose that n = 10 and the sampled serving times (in seconds) are recorded as follows