Arti wrote to us to say:

There are two things that are not defined which need a definition:
- If player A marked a number in the number line, can player B mark it later?
- If player A used two numbers from the square, can player B use one or both those numbers?

These are excellent questions, Arti.  I'd be interested to know what you decided.  To start with, I think I'd try to play with the rules that once a number has been marked, it can't be marked again later and that it doesn't matter which numbers your partner chooses, you can choose any you like.  But perhaps you decided differently?

Rowena from Christ Church Primary told us:

I played this game with my Mum and neither of us won. We played it again and my Mum let me win!
We decided to list all the possible whole number answers. They were 2, 3, 4, 5, 6, 8, 9, 10, 12, 15 and 20. Once we knew these, it was easy to choose numbers to block the opponent and not let them get 4 in a row.
You can only win if your opponent makes a mistake or lets you win!

Thank you, Rowena - a good idea to make a list of the whole number answers.

I wonder whether you could change the game so that it was easier to win?