This is called the Monty Problem. The bit possibly not explained is that in the game, the host opening the door KNOWS which door has the car, and purposely opens one that has a goat. So now you have more information. When you choose door 1 initially, there is a 33% chance of a car in it, and 66% chance of goat. So now that host has to open a door, and if you have a goat in door 1, the host only has 1 door option to open. If you have a car, they have 2 door options. So you are better off switching, because there is a 66% chance you have a goat, and the host just revealed with other door has a goat.
Wikipedia has a table which makes it more intuitive to see the possibilities.
This is called the Monty Problem. The bit possibly not explained is that in the game, the host opening the door KNOWS which door has the car, and purposely opens one that has a goat. So now you have more information. When you choose door 1 initially, there is a 33% chance of a car in it, and 66% chance of goat. So now that host has to open a door, and if you have a goat in door 1, the host only has 1 door option to open. If you have a car, they have 2 door options. So you are better off switching, because there is a 66% chance you have a goat, and the host just revealed with other door has a goat. Wikipedia has a table which makes it more intuitive to see the possibilities.