getGPA in Google spreadsheet

function getGPA(weight, grade, sumWeight) {
  var gpa = 0;
  for (var i = 0; i < weight.length; i++){
    if ( grade[i] != 'i' && grade[i] != 'I') {
      gpa = gpa + (weight[i] * grade[i]);
    }
  }
  return gpa/sumWeight;
}