How many signs?
How many different signs are there? Or, to make the question slightly more definite, how many signs can you make with 1 circle, 2 circles, 3 circles, and so on? In general, how many signs can you make with n circles?
Here are the answers up to n=4 circles (not forgetting n=0):
You may like to work out a few more for yourself. In case you do, the results for n=5,6,... etc are not given here, but are to be found on the next page.