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Choose a domino set with a double-12 for a 13-hand game; choose the double-9 set for a 10-hand game. From whichever set you choose, remove the highest double-sided tile before you move on to shuffling. In Mexican Train, the game starts with the highest double-sided tile in the middle of the table. Each hand after that starts with the double-sided tile that is one number less than the one preceding it: the first hand starts with the double-12, the second hand starts with the double-11, the third hand starts with the double-10, and so on. Lay out all of the tiles and flip them so they are pip-side down. Thoroughly mix them up by hand. Because there are so many rounds played in Mexican Train, have players take turns flipping and shuffling the tiles. After you draw your tiles, set them up in front of you on their sides so you can see what you have, but try your best to keep them hidden from your neighbors. You can play Mexican train with up to 8 people if you have a double-12 set. If you have a double-9 set, you can play with only 2 to 4 people. Follow this breakdown to determine how many tiles each person should take:  Double-12: 2 to 3 players take 16 tiles each; 4 players take 15 tiles each; 5 players take 14 tiles each; 6 players take 12 tiles each; 7 players take 10 tiles each; 8 players take 9 tiles each. Double-9: 2 players take 15 tiles each; 3 players take 13 tiles each; 4 players take 10 tiles each. If on any given turn you don't have a domino in your hand that can be played on either the Mexican train or your personal train, draw one tile from the train yard. If that tile can be played, play it. If not, it gets added to your hand and the turn passes on to the next player.  The “train yard” is also sometimes called the “bone pile.” Keep the tiles in the train yard face down. After drawing tiles for your hand and creating the train yard, it's finally time for gameplay to begin! There are sets you can buy that include a little stand for the starter tile, which you're welcome to use if you have it. If not, simply place the double-12 or double-9 tile into the center of the playing space.  This starter tile is often referred to as the “engine tile.” Everyone can play off of the engine tile, though each person's personal train coming off of that engine tile isn't fair game to other players unless there is a marker on it, which appears when a player isn't able to take their turn. Whoever goes first can lay down a tile only if they have one that matches the denomination of the engine tile. For example, if the engine tile is a double-12, then you must lay down a tile that has 12 pips on one side or the other. The 12-pip side needs to be laid down so it is connected to the double-12 engine tile. The exception to the 1-tile per turn rule is if you lay down a double tile, meaning that the pips on each side of the tile are the same. If you lay down a double tile, take a second turn immediately and lay down an additional tile. Once a player has laid down all the tiles in their hand, that particular round is over. Keep score on a piece of paper; have each player with tiles left in their hand add up the total number of pips. Add this figure beneath their name on the scoresheet. The goal is to have the lowest number at the end of all the rounds.  A set of double-12 dominoes will have 13 rounds, and a set of double-9 dominoes will have 10 rounds. The only other way a round can end is if the entire train yard has been depleted and no one can make a move. In that case, everyone tallies up the pips left in their hand and those figures get added to the score sheet. Each new round is started with the engine tile that is one number lower than the one used in the previous hand (double-9 for the first hand, double-8 for the second hand, double-7 for the third, and so on). The blank double is the last engine you will use before the end of the game (blank tiles can only be matched with tiles that also have a blank side). The already-used double tiles just get mixed back in with the other tiles when you shuffle between rounds.
Pull out the double-12 or double-9 domino from the set. Shuffle the remaining dominoes facedown on the table in front of you. Have each player draw their cards from the shuffled tiles. Put the remaining tiles into the “train yard” to draw from on future turns. Set the double domino in the center of the table to begin play. Pick someone to start and take turns clockwise around the table. Win a hand by being the first to lay down all of your dominoes. Continue playing and keeping score until all the double tiles are used.