Question 3 The length of time which an ordinary light bulb will last may be taken to have mean 600 hours and variance 9604 hours. (a) Two ordinary bulbs are chosen. Calculate the probability that only one of the bulbs will last between 450 and 520 hours. (7 marks] (b) lOne hundred ordinary bulbs are chosen at random. Calculate the probability that the mean of the times for which they last more than 595 hours. (5 marks) (TOTAL: 12 marks)