Question counter doesn't seem to work + feedback on my code?

/* CHALLENGE INSTRUCTIONS
1. Ask at least five questions
2. Keep track of the number of questions the user answered correctly
3. Provide a final message after the quiz letting the user know the number of questions he or she got right.
4. Rank the player. If the player answered all five correctly, give that player the gold crown: 3-4 is a silver crown; 1-2 correct answers is a bronze crown and 0 correct is no crown at all.
*/

/* Challenge Question + Answer 
1. Where stands WWW for?  World Wide Web
2. What is the color black in CSS?  #000
3. What is 101 in binary code?  5
4. The brain of a computer is?  CPU
5. Mega Byte is equel to? 1024 Kilo Bytes
*/

// Start Quiz
console.log("Start Quiz");


// Score
var answer = 0;

// Counter questions remaining
var questions = 5;
var questionsLeft = "[" + questions + " " + "questions left]";


// Question 1
var questionOne = prompt("Where stands WWW for?" + questionsLeft);
if (questionOne.toUpperCase()  === "World Wide Web") {
  alert("You're correct!");
  answer += 1;
  questions -= 1; 
  questionsLeft = '[' + questions + ' questions left]';
} else {
  alert('Sorry, this is incorrect.');
}

// Question 2
var questionTwo = prompt("What is the color black in CSS?" + questionsLeft);
if (questionTwo.toUpperCase() === "#000") {
  alert("You're correct!");
  answer += 1;
  questions -= 1; 
  questionsLeft = '[' + questions + ' questions left]';
} else {
  alert('Sorry, this is incorrect.');   
}

// Question 3
var questionThree = prompt("What is 101 in binary code?" + questionsLeft);
if (parseInt(questionThree) === 5) {
  alert("You're correct!");
  answer += 1;
  questions -= 1; 
  questionsLeft = '[' + questions + ' questions left]';
} else {
  alert('Sorry, this is incorrect.');
}

// Question 4
var questionFour = prompt("The brain of a computer is?" + questionsLeft);
if (questionFour.toUpperCase() === "CPU") {
  alert("You're correct!");
  answer += 1;
  questions -= 1; 
  questionsLeft = '[' + questions + ' questions left]';
} else {
  alert('Sorry, this is incorrect.');
}

// Question 5 
var questionFive = prompt("Mega Byte is equel to?" + questionsLeft);
if ( questionFive.toUpperCase() === "1024 Kilo Bytes") {
  alert("You're correct!");
  answer += 1;
  questions -= 1; 
  questionsLeft = '[' + questions + ' questions left]';
} else {
  alert('Sorry, this is incorrect.');
}

// Ranking the player based on his score
if (answer === 5) {
  document.write("<p>You have won a GOLDEN CROWN!</p>");    
} else if (answer <= 4 && answer >= 3) {
  document.write("<p>You have won a SILVER CROWN!</p>");  
} else if (answer <=2 && answer >= 1){
  document.write("<p>You have won a Bronze Crown!</p>");
} else if (answer === 0) {
  document.write("<p>Sorry, You didn't win a Crown.</p>");
}


// Displaying the final score
var finalResult = alert("Congratulations you answered " + answer + " questions correctly!");


// End Quiz
console.log("End Quiz");