A company wishes to check on the efficiency of its call centre. It carries out checks on a sample of 200 customer calls by using computer monitoring equipment which measures the length of calls.

i) true population mean time per call = 2.3 minutes, standard deviation = 1.28 minutes.

what is the probability that the mean of this sample will be less than 2.1 minutes?

ii) how do we answer i) without knowing if the population call time distribution is skewed or not?