a)Find, using formula, the point estimate of the mean and variance of mercury concentration after the accident to 4 decimal places. (3 marks) b)Construct a 95% condence interval for the true standard deviation of mercury concentration after the accident. Interpret the interval obtained.(5 marks) c) Based on the interval in (b), can you conclude that a change in the standard deviation has occurred after the accident at 95% condence level? Explain your answer. (2 marks) d) Is there sufcient evidence to support that the mean mercury concentration has increased after the accident? Test at 5% level of signicance. (5 marks) 1.60 1.77 1.61 1.08 1.07 1.79 1.34 1.07 1.45 1.59 1.43 2.07 1.16 0.85 2.11 Fifteen measurements were taken and recorded as follows. The concentration of mercury in a lake has been monitored for several years. The measurements taken on weekly basis yielded an average and standard deviation of 1.20 mg/m3 (milligrams per cubic meter) and 0.285 mg/m3, respectively. The measurements are normally distributed. An accident occurred at a smelter on the shore of the lake, which causes the mercury concentration level to change