I use this "trick" with students who know their basic math but need to increase their speed and accuracy. I play "math war". It is based on the card game war, but builds math speed. The basics:

Remove all face cards (leave the Aces)

Deal the cards as you would in the game "war"

Players flip the top card and the first player to call out the sum of the cards wins that round

Count the number of cards at the end.

The best thing is that it can be modified to "odds/evens" (is the sum odd or even) or even multiplication.

They can build their speed and still play the game. It can be modified to more than 2 players or many other ways.

Hope this helps and gives some ideas

Mike