<form name="form1">
<label for="ans0">
<input type="radio" name="answer" id="ans0" value=0>
</label>
<input type="button" id="next" value="Next">
<input type="button" id="back" value="Back">
</form>
....
function nextClick(){
  //jots down answers
  answerSheet[currentQuestion] = $("#form1 input[name='answer']:checked").val();
  ...
  currentQuestion++;
  populateQA();
  ...
}
function populateQA(){
  //code to replace question and answers from an array
}
function backClick(){
  currentQuestion--;                 // Navigates to the last question
  var prevAns = answerSheet[currentQuestion];
  alert(prevAns);                    // my test
  $("#form1 input[value=" + prevAns + "]").attr("checked", true);
  populateQA();
}
var currentQuestion = 0;
var answerSheet = [];
...
$("#next").on("click", nextClick);
$("#back#).on("click", backClick);

$("#form1 input[value=" + prevAns + "]").attr("checked", true);