MODEL:
! Model of a queuing system with N servers, each of
  which costs $17/hour. Arrivals occur at a rate of 
  70 per hour in a Poisson stream. Arrivals finding
  all servers busy are lost. A lost customer costs 
  $35. The average time to process a customer is 5 
  minutes;

! Minimize total cost = 
  service costs + lost customer cost;
    [COST]  MIN = SCOST + LCOST ;

! Cost of servers;
    SCOST = 17 * N ;

! Cost of lost customers;
    LCOST = 35 * 70 * FLOST ;

! The fraction of customers lost;
    FLOST = @PEL( 70 * 5 / 60 , N);
END