A bank manager is trying to estimate the amount of fraud that will happen on a day when cyber crooks break into the bank's Website and many hackers collaboratively create a flood of frauds. So he starts counting the number of frauds that happen in a day and plans to use 95% confidence level. He observes the data for 100 days. The mean fraud per day for the hundred days (n = 100) is 5.3 and std. dev. of his data is 1.2. Standard deviation of whole hacker population is unknown. Which of the following statement/s is correct?
A The manager does not know enough about normal distribution
B The manager should use t statistic to estimate the confidence interval
C We are 5% confident that the true mean is in the confidence interval calculated
D The manager cannot use 95% confidence level because it is too low