Many of you sent in excellent solutions to this problem. You tackled it using algebra, in other words using a letter to represent the number that you started with. Thank you to all pupils from Ardingly College who answered the problem in this way, and to Bronya and Caroline from Tattingstone School. Here is Alistair's solution. Alistair, who goes to Histon Junior School, has explained the algebraic steps very clearly:

If X is the number you think of, you start with X
Then when you add 1, you get X + 1
When you double it, it turns into 2X + 2
When you take away 3, it turns into 2X -1
Adding the number you first thought of makes 3X -1
When you add 7 it turns into 3X + 6
When you divide by 3 it turns into 1X + 2
Then take away the number you first thought of (X) it leaves 2.