This is a game for two players.
You could start with 12 biscuits (or buttons, or pebbles, or…) and put four biscuits (or buttons, or pebbles, or…) into one jar and eight into the other jar (you just need to make two groups).
Each player can take biscuits in one of two ways:
1. By taking any number they like from just one jar or
2. By taking the same amount from both jars.
The winner is the person who takes the last biscuit/s.
Think carefully! See if you can discover a winning strategy before your friends do.