I was helping someone on a Game Design Forum with how to figure out what cards and how many of each you need in your deck. I decided that I should include that post here with a bit more detail. Sorry for the long post, I try not to make my posts this large, but it is a lot of info to convey.
My game that has 3 separate decks of cards and each deck has multiple uses based on various factors. Each deck is about 32-48 cards each.
Each one of my decks has different numbers of cards and different uses based on the situation they are drawn from. For it to be balanced, I needed to find the numbers of each card, turn that into a percentage of the total deck, and make adjustments from there. The best way to do this is my opinion is with excel (or Pages if you use a Mac). You can also use Google Spreadsheet since its web based and can be accessed from both Mac and PC.
Here is my spreadsheet that I used. This shows my Cargo type (Column E) and the cities merchants can travel to (Column F). You will need to build some formulas that look something like: =TO_PERCENT (G3/G19) Shown in RED in upper left. Where G3 is the Number of Cards of a specific type and G19 is the total number of cards in your deck. This will display a percentage like (in this example from my deck) 13%. The next card would look like this =TO_PERCENT (G4/G19). Notice that the G4 is the only thing that has changed. This is comparing this number of cards against the total number of cards in your deck.
The other important thing is to make the columns (is this example G and H sown in Yellow) add up to a TOTAL (G19 and H19). This will make it so that if you ever make a change, the percentage will be automatically updated whenever you add or remove card numbers.
You will want to be carful about how many cards you have in a deck, it can be very easy to throw to much into it or have to many duplicates of a card.
Now where these cards got complicated was that I had the second values that each card could do. In this example the Cargo Cards are drawn when an Event Card requires a random city to be effected by the Event. To make it fair, I needed a relatively even distribution of Cities over an uneven distribution of cards. So yo can see there are duplicate Cargos with different Cities in Column E and F. On the far right is my total number of Cards for each city (Column I and J). Its not 100% perfect, two cities only ended with 6 instead of 5. To make this work out, I chose the two cities farthest away from each other, making Events slightly more likely to happen more evenly distributed across the board.
To find the right number, that is a bit of trial and error. In general, I like to start with a low number of each card and expand from there. Inevitably you will find cards that you had not thought of. It very important that you do not add everything. What you don't add is just as important as what you do add. Ask yourself this question: "Do I need this for my game, or do I just want this"? Is the sign of a good designer to show restraint....its not always easy and we often add things because we want them, but down the road come to realize that they are causing more problems. In the end, as sad as it makes you, you pull it from the game because it makes it better and stronger design.