สอบถามการนำ Array มาบวกกันไม่ได้ตามที่ต้องการ ทำยังไงครับ?

<script type="text/javascript">
var myArray1 = new Array(3);

  for (i = 0; i < 3; i++){
      myArray1[i] = new Array(3);
    }

  myArray1[0][0] = "1";
  myArray1[0][1] = "3";
  myArray1[0][2] = "5";

  myArray1[1][0] = "0.333";
  myArray1[1][1] = "1";
  myArray1[1][2] = "3";

  myArray1[2][0] = "0.2";
  myArray1[2][1] = "0.333";
  myArray1[2][2] = "1";

  a = myArray1[0][0] + myArray1[1][0] + myArray1[2][0];
  b = myArray1[0][1] + myArray1[1][1] + myArray1[2][1];
  c = myArray1[0][2] + myArray1[1][2] + myArray1[2][2];

  document.write(a);

</script>