单项选择题 Penny Bauer, Chief Financial Officer of Harrison Haulage, suspects irregularities in the payroll system, and orders an inspection of ‘each and every payroll voucher issued since 1 January 2005’. Five per cent of the payroll vouchers contained material errors. This is an example of （）.

判断题 Statistical independence means the outcome of one event is independent of the outcome of a second event.

判断题 If the population distribution is unknown, in most cases the sampling distribution of the mean can be approximated by the normal distribution if the sample size is at least 15 observations.