You certainly know the popular 24 Game, in which you're given four 1 to 9 numbers and the objective is to come up with some combination of arithmetic operations that will end up using all the numbers and which the result is 24. In my country there are (or used to be) some serious tournaments around it and I had the chance to reach a regional stage of the national tournament when I was in my 6th grade. However, my school didn't had that much cards so my training was limited because no matter how good you are at math the memory part of the brain will always reach the solution to a puzzle before the arithmetic part does a single operation, so having less cards means less memorization/training.
So recently, as my brother now reaches that level I just thought I could put in practice my programming skills (which would have been very helpful if I had them back then) and generate all the possible cards for that game. The program returns exactly 195 390 unique cards and presents the way of solving (there could be others). Just take it, memorize it and do your best if there are some tournaments you can participate in.
Click to browse all the cards
EDIT: My friend Pedro Diogo (many thanks to him) took the data and created ready to print cards. So,
Click here to download the ready to print cards.
If you want to check out the code feel free to here.
Regarding that game, I lost against the national winner and his trick was exactly that, he just memorized the cards and how to solve them. The only card he lost, was one he couldn't remember and i had my chance to think for a while (which he didn't). Later he told me in his school they would be memorizing cards all the time, even in classes. I just don't get the fun of it anymore :(