The Human Resources department of a large company wants to be able to plan for the amount of time employees will need to complete a compulsory online training course about the company's health and safety policies. A random sample of 20 staff is selected. The time taken by each of them to complete the training is recorded. The sample average is 74 minutes, and the sample standard deviation is 53 minutes.

(a)Find a 95% confidence interval for the population average time to complete the training. [10 marks]

(b)Identify any assumptions that you need to make. 5marks