Answer:
The number is  [tex](S \ u \ C ) = 649[/tex]
Step-by-step explanation:
From the question we are told that Â
   The sample size is  n =  800
    The number of seniors is  S  =  519
     The number of  commuters is  C =  430
     The number of of seniors that are commuters is  [tex](S\ n \ C )= 300[/tex]
Generally the number of 800 surveyed students who were seniors or were commuters is  mathematically evaluated as
   [tex](S \ u \ C ) = S + C - ( S \ n \ C )[/tex]
=> Â [tex](S \ u \ C ) = 519 + 430 - 300[/tex]
=> Â [tex](S \ u \ C ) = 649[/tex]