Here's how I did it :)

function print(message) {
  document.write(message);
}

var numCorrect = 0;
var resultsHTML = '';
var correctHTML = '<h2>You got these questions correct:</h2><ol>';
var incorrectHTML = '<h2>You got these questions wrong:</h2><ol>';

var questions = [
  [ 'How many states are in the United States?', 50 ],
  [ 'How many legs does an insect have?', 6 ],
  [ 'How many continent are there?', 7 ]
];


//ask questions by looping through questions
for ( var i = 0; i < questions.length; i++) {

  //get the question from array
  var question = questions[i][0];

  //get the answer from array
  var correctAnswer = questions[i][1];

  //prompt user for answer to question
  var userAnswer = prompt(question);
  userAnswer = parseInt(userAnswer);

  //evaluate userAnswer
  if ( userAnswer === correctAnswer ) {
    // add 1 to numCorrect
    numCorrect++;
    // add question to correctHTML as a list item
    correctHTML += '<li>' + question + '</li>';
  } else {
    // add question to incorrectHTML as a list item
    incorrectHTML += '<li>' + question + '</li>';
  } 
}

correctHTML += '</ol>';
incorrectHTML += '</ol>';

if ( numCorrect && numCorrect === questions.length ) {
  resultsHTML += '<p>You got all ' + questions.length + ' questions right!</p>';
} else if ( numCorrect ) {
  resultsHTML += '<p>You got ' + numCorrect + ' question(s) right.</p>';
} else {
  resultsHTML += '<p>You got them all wrong!</p>';
}

if ( numCorrect ) {
  resultsHTML += correctHTML;
}

if ( numCorrect < questions.length ) {
  resultsHTML += incorrectHTML;
}

print(resultsHTML);