Problem 11.1. Inside a circle, 16 radii of the circle and 10 concentric circles, whose centers coincide with the center of the circle, are drawn. Into how many regions do the radii and circles divide the circle?
Answer: 176.

Solution. 10 circles divide the circle into 10 rings and one smaller circle, a total of 11 parts. 16 radii divide each of the 11 parts into 16 more. In total, there are $11 \cdot 16=176$ regions.