A research paper studies how long coronaviruses can survive on surfaces, such as tables and door handles. The study shows that the average survival time of coronaviruses is 48 hours, with a standard deviation of 12 hours. For the following 3 questions, please consider a sample of the virus. We randomly obtain some sample of the virus, observe the survival time of each of the virus, and calculate the average survival time of all the viruses in the sample.