A computer system administrator notices that computers running a particular operating system seem to crash more often as the installation of the operating system ages. She measures the time (in minutes) before crash for five computers one month after installation, and for nine computers seven months after installation. The results are as follows:
One month after installation
209 230 217 230 221 243 247
Seven months after installation
85 59 129 201 176 240 149 154 105
(a) Explain why it is necessary to check whether the populations are approximately normal before constructing a confidence level?