There's nothing like trying it experimentally. Direct experience is most convincing.
Equipment Grab a whole bunch of quarters and pennies.
These represent the two goats and the car, but we're going to keep all our prizes in this experiment, so we'll need a good supply. Go ahead and use them. If you are farmer or otherwise rurally inclined, you may use real goats, however we have found this to be troublesome. Find three small boxes , or envelopes or books or any other object convenient for hiding the coins in or under. Three of them, to represent the three doors.