Age 7 to 11
Remember that you must have two or more sticks to make a set.
Try starting with a set of $2$. How many sticks would be in the set
placed across these $2$? How many crossings would that make?
If you can't have a set of $1$ stick, what number could you try
Do you notice anything about the number of sticks in each set and
the number of crossings? How do these numbers relate to the total
number of sticks?