There are four games in this powerpoint. It is an adaptation of a class game that I play on the whiteboard and works in the same way that Noughts and Crosses work. The object is to get 3 noughts or 3 crosses in a row but the students have to get answers correct in order to gain the nought or cross.
Divide the class in half (or play one group against another). The sides take turns to answer the questions and never have two turns in a row.
If an answer is correct then click on a tile to show the answer below, click on the tile again for an X, click again for a O. It's very easy to play but make sure you have a little play with it before playing it with your class.
You may need to develop your own rules depending on the class but there is more information about that on the second slide.
There are four games here. Every second slide is a set of answers which you should probably print out before you play but you don't really have to if you have the inclination to work out the answers on the spot. The games become increasingly more difficult but they are still reasonable enough for mental calculations (or students can use a calculator).
The operations involve fractions, decimals, percentages, percentage of, increase and decrease by a percentage, share in a ratio etc
There is another set of games which are slightly easier: https://www.teacherspayteachers.com/items/edit/2756204