In a sample of 18 kids, their mean time on the internet on the phone was 28.6 hours with a sample standard deviation of 5.6 hours. Which distribution would be most appropriate to use, When we assume these times are normally distributed? Homework Help. 5VC. Using z or t (2:13) t distribution as the population standard deviation is unknown while the times are assumed to be normally distributed 2 distribution as the population standard deviation is known while the times are assumed to be normally distributed mintdistribution as the sample standard deviation is unknown z distribution as the sample standard deviation always represents the population