The Monty Hall Problem is a probability puzzle that has intrigued and baffled people for decades. It is named after Monty Hall, the original host of the American television game show “Let’s Make a Deal.” This problem presents a scenario that defies intuitive reasoning, challenging our understanding of probability and decision-making. Read on as we explore the intricacies of this seemingly paradoxical problem.

The Problem Setup

Imagine you are a contestant on a game show. There are three doors: behind one door is a car (the prize you want), and behind the other two doors are goats (the prizes you don’t want). You do not know what is behind any of the doors. Here’s how the game works:

1. You pick one of the three doors.

2. The host, Monty Hall, knows what is behind all the doors and opens one of the other two doors. He will always reveal a goat.

3. Monty now asks you if you want to stick with your original choice or switch to the remaining unopened door.

Should you stick with your initial choice or switch to the other door? Or does it not matter?

Initial Intuition

Most people’s initial intuition is that it does not matter whether they switch or stick; they assume the odds are 50-50 because two doors remain, one hiding the car and the other a goat.

This intuitive assumption, however, is incorrect. The correct strategy is to always switch doors, which gives you a 2/3 chance of winning the car, compared to a 1/3 chance if you stick with your initial choice.

Breaking Down the Probability

To understand why switching is the better strategy, let’s break down the probabilities:

1. Choosing the Door: Initially, there is a 1/3 chance you pick the car and a 2/3 chance you pick a goat.

2. Monty Opens a Door: Monty will always reveal a goat. If you initially picked the car (1/3 chance), Monty has two goats to choose from. If you initially picked a goat (2/3 chance), Monty has only one door he can open.

Here’s the key insight:

  • If you picked the car (1/3 probability), switching results in a loss because the remaining door has a goat.
  • If you picked a goat (2/3 probability), switching results in a win because the remaining door has the car.

Thus, switching doors means you win the car 2/3 of the time.


  • The host must always open a door that was not selected by the contestant.
  • The host must always open a door to reveal a goat and never the car.
  • The host must always offer the chance to switch between the door chosen originally and the closed door remaining.

Detailed Scenarios

To further clarify, consider the detailed scenarios:

Scenario 1: Car Behind Door 1

  • You choose Door 1.
  • Monty opens Door 2 or 3 (both have goats).
  • If you switch, you lose (car was behind your original choice).

Scenario 2: Goat Behind Door 1, Car Behind Door 2

  • You choose Door 1.
  • Monty opens Door 3 (goat).
  • If you switch, you win (car behind Door 2).

Scenario 3: Goat Behind Door 1, Car Behind Door 3

  • You choose Door 1.
  • Monty opens Door 2 (goat).
  • If you switch, you win (car behind Door 3).

In two out of the three scenarios, switching wins the car, confirming the 2/3 probability.

Common Misunderstandings

Several misunderstandings contribute to the intuitive but incorrect belief that the probabilities are equal after Monty opens a door:

1. Equal Probabilities Fallacy: The mistake lies in assuming the two remaining doors each have an equal chance of hiding the car after Monty’s reveal. This is not the case; the initial choice still influences the probabilities.

2. Neglecting Monty’s Knowledge: Monty’s knowledge and his deliberate action to reveal a goat are crucial. The assumption of independence does not hold, as Monty’s choice is not random but informed. This affects the probability distribution.

Psychological Aspects

The Monty Hall Problem also highlights interesting psychological phenomena:

  • Confirmation Bias: People often seek information that confirms their initial beliefs. The 50-50 intuition is strongly held, so people tend to ignore explanations that contradict it.
  • Cognitive Dissonance: Accepting the correct solution often requires overcoming cognitive dissonance, as it contradicts our ingrained intuitions about probability and fairness.
  • Simulation Aversion: Many people resist running simulations or using mathematical proofs, preferring to rely on gut feelings, which can mislead them in probabilistic situations.

Educational Value

The Monty Hall Problem is a valuable educational tool. It encourages:

  • Critical Thinking: Challenging students to question their intuitions and explore the logical underpinnings of probability.
  • Problem-Solving Skills: Applying mathematical concepts to real-world scenarios and understanding complex probability distributions.
  • Appreciation for Counterintuitive Results: Demonstrating that intuition can sometimes lead us astray and rigorous analysis is necessary.


The Monty Hall Problem is a fascinating illustration of how probability can defy our expectations. By switching doors, contestants can significantly increase their chances of winning the car from 1/3 to 2/3. This puzzle underscores the importance of understanding the underlying principles of probability rather than relying on intuition alone. It continues to be a topic of interest and discussion, serving as a powerful example of the counterintuitive nature of probability theory.

Interested in exploring more mathematical puzzles? Why not join us at Miracle Math? With the assistance of our primary and secondary mathematics tutor in Singapore, you are sure to ace your next tests and exams. Contact us for more information.