For those who don't get it, here is an explanation using the three options you can choose from:
1) Pick a door with a goat. Host reveals other goat. Switching wins.
2) Pick a door with a goat (the other one). Host reveals other goat. Switching wins.
3) Pick a door with a car. Host reveals one of the other doors (they both have goats). Switching loses.
The idea is that you have a 2/3 chance of picking a door with a goat at the start, so you are more to have picked a goat. When you have picked a goat, switching always wins. If you picked a car at the beginning, switching will always lose, but since you only have a 1/3 chance of picking a car at the start, the chances are against you. On the other hand, if you stay with your choice, 2/3 times you will lose, and 1/3 times you will win.
So it is more advantageous to switch
1) Pick a door with a goat. Host reveals other goat. Switching wins.
2) Pick a door with a goat (the other one). Host reveals other goat. Switching wins.
3) Pick a door with a car. Host reveals one of the other doors (they both have goats). Switching loses.
The idea is that you have a 2/3 chance of picking a door with a goat at the start, so you are more to have picked a goat. When you have picked a goat, switching always wins. If you picked a car at the beginning, switching will always lose, but since you only have a 1/3 chance of picking a car at the start, the chances are against you. On the other hand, if you stay with your choice, 2/3 times you will lose, and 1/3 times you will win.
So it is more advantageous to switch
