Which type of sampling method is being employed in the following example: "The principal of Phoenix High School is conducting an in depth study of the
graduates since she has been there. First, she creates a list of every student that has
graduated since she has been principal and assigns each graduate a number 1 to
1241. She, then has a computer randomly select 40 numbers between 1 and 1241
to determine which students she will include in her sample."