var numQues = 20;
var numChoi = 2;

var answers = new Array(20);
answers[0] = "yes";
answers[1] = "yes";
answers[2] = "yes";
answers[3] = "yes";
answers[4] = "yes";
answers[5] = "yes";
answers[6] = "yes";
answers[7] = "Yes";
answers[8] = "yes";
answers[9] = "yes";
answers[10] = "yes";
answers[11] = "yes";
answers[12] = "Yes";
answers[13] = "yes";
answers[14] = "Yes";
answers[15] = "yes";
answers[16] = "yes";
answers[17] = "yes";
answers[18] = "Yes";
answers[19] = "yes";
answers[20] = "Yes";

function getScore(form) {
  var score = 0;
  var currElt;
  var currSelection;

  for (i=0; i<numQues; i++) {
    currElt = i*numChoi;
    for (j=0; j<numChoi; j++) {
      currSelection = form.elements[currElt + j];
      if (currSelection.checked) {
        if (currSelection.value == answers[i]) {
          score++;
          break;
        }
      }
    }
  }

  score = Math.round(score/numQues*100);
  form.percentage.value = score + "%";

 
}