As this activity is for groups to work on and there are all sorts of possible outcomes, we haven't received many solutions.
However, Nathan from St. Helen's School in Abbotsham sent in this clear account with some suggestions:
We played counters in the middle - we thought it can be very tricky but when you get closer it gets so much easier.
Firstly we guessed the first counter and then the last counter.
After we got them right we had some counters in front of us. We used them to guess what some of the others were - you would be suprised about how much easier this is.
Good questions:
Has it got a pattern?
How many colours have you used?
How many counters are there?
How many blue counters have you used?
Less useful questions:
Is it red?
Danny, Aaron, Emma, Emily and Ella from Bacton Community Primary School sent in these comments:
What if you asked them what colours they have got.
Ask the shades of colours as well and how many. If you know your partner's favourite colour then you have a big advantage. Working in a team helps a lot as well as being good friends.
Thank you for these comments and suggestions, which will be useful to others reading this before trying the activity!