According to a mashable post, time spent on tumblr, a microblogging platform and social networking website, has a mean of 14 minutes per visit. (source: on. mash. to/1757wfe.) as- sume that time spent on tumblr per visit is normally distributed and that the standard deviation is 4 minutes. if you select a random sample of 25 visits, a. what is the probability that the sample mean is between 13.6 and 14.4 minutes

Solution: We are given that the time spent on tumblr, a microblogging platform and social networking website is normally distributed with mean = 14 minutes and standard deviation = 4 minutes

We have to find, If we select a random sample of 25 visits,  the probability that the sample mean is between 13.6 and 14.4 minutes. In other words, we have to find:

First we have to find the z scores as:

Using the standard normal table, we have:

Therefore, if a random sample of 25 visits is selected, the probability that the sample mean is between 13.6 and 14.4 minutes is 0.3830