BEGIN { sum1=0 ; average1=0; noPeople1=0
   sum2=0 ; average2=0; noPeople2=0
 }

{  
  if ( $3 == "F" )
   {
   print $0   
   noPeople1++ 
   sum1 += $4 ;
  } 
 else if ( $3 == "M" )
  {
   print $0   
   noPeople2++ 
   sum2 += $4 ;
  }

}

END { print "Average marks for F:", sum1/noPeople1
print "Average marks for M:", sum2/noPeople2
  }