This is very similar to war, but each student flips two cards. They either add them, subtract them, multiply them, or put them into fractions...whatever you are currently working on. Then after they find the sum, difference, etc. then they compare to the other person's cards. The person with the higher amount says, "I have _____. You have _____. _____ is greater than ______." Then they get to keep the cards. If they are equivalent, then they just keep their own cards.

each person flips two cards (ex. 3 and 7)
arrange cards to make largest number (73)
now....your score for this round is how far away from 100 you are (100-73=27) score 27
continue until someone reaches a score of 100

race to 100 with addition
flip one card at a time....continue adding one digit numbers until you reach 100

or increase it to race to 500
flip two cards...add two-digit numbers until you get to 500

I do this whole class, but you can also do it as a center. Each student has a piece of paper that they fold to create boxes, we usually do 8 boxes with a half size sheet of paper. They unfold it, then in the first box, put a line for each place value you want to practice to. For example, if you want to practice to the thousands place,
you put _ _ _ _ in the box.

Next, one person calls either greatest value or least value for the round.

Then, you display one card at a time. Each student playing has to make a decision about where to place it to make the largest or smallest number they can. It's also important that they use a crayon, marker or pen for this game so that they can't change their answer!

After everyone playing writes the digit drawn on their paper, another card is drawn and the procedure is repeated. When all the places are filled, they sort the playing cards drawn into the correct order for the round, least or greatest and then a winner is declared.

I don't even emphasize the winning part but we do talk about why we place the digits to achieve the best answer and how probability plays into the game. It's easy to learn to play and it really gets them thinking about the value of the digit. My students really like it.

Here's a list someone (sorry, I don't have a name to give credit to) posted awhile back with lots of math skill card games. I saved it because it had so many great ideas.