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EN 
The cards offered in the commercial building to buy or upgrade attacks change every 3 days.
The usual purchase price of the cards is not linear, i.e. when you buy the first one, the second one increases the initial value according to the type of disaster the card belongs to. For example, in Magnetism cards -which belongs to common aquamarine disasters- (as seen in the picture on the left), the initial price is 15 bills (SimCash) for the first card you buy, the second one costs 16, the third one 17, and so on up to a maximum of 20 cards (depending on the field you are in). But in addition, when you buy rare disaster cards (amber color), the initial card is worth 50 (as seen in the picture on the left), but the second card increases its value by 5 SimCash, costing 55, the third 60, and so on up to a maximum of 10 cards. In the legendary disasters it is even worse, the initial price is 120 SimCash, and the increase is 10.
However, if you change club with different level of War (it is also often called arena or field), the price of the cards reset their value. That is to say, if you want to buy 4 magnetism cards, buy only 1 in your club, which will cost you 15 SimCash, change club with a different level and you will see that it is 15 SimCash again, buy another one. Repeat the operation with two other clubs with different levels to the previous ones. In this case you will have saved 3 tickets. But in the case of buying 10 cards, the saving can be 9+8+7+6+5+5+4+3+2+1-1-1-1-1-1 = 40 SimCash, and so on in geometric progression.
Important: choose clubs where to go with few members (less than 9) so that while you do the operation of buying cards, do not activate a war and get trapped in a foreign club.
It is also important to let your club know that you are going out to buy cards, so that, among other things, they do not start a battle without you or they are waiting for you to open if the club is private.
