Thank you to everyone who sent in a solution to this problem. Most of you agreed that there was just one piece of string in the first picture, two in the second, one in the third and two in the fourth.
Thomas from St Luke's School in Frodsham explained how he worked out the number of pieces of string in the last picture:I started at one point, followed the string round in one direction and found that I came back to where I started. I realised that I hadn't been everywhere, so I started from a place that I hadn't been and went around again. When I got back to the start again, I had been everywhere, so there are two loops.
This is very clear - thank you Luke.
Well done also to Diana, Kate and Georgia from Danebank School who also wrote clear explanations of how they counted the pieces of string.