How old?

Riddle: How can you use a length of wool to estimate the age of a tree?

We had a fun afternoon trying to find out, first off by using our tree identification books (not as easy as you might think), to find out growth rates and then some of the Montessori maths' materials.

On reflection, I'm not sure we got the formula right for our maths work. We need to revisit, as the logic before our eyes suggests strongly that the trees are older than 6 years!