This picture is taken from the Problem Pictures resource of photographs with activities for mathematics teaching.
If you purchase this resource the photographs are available in higher resolution and there are additional pages containing hints and solutions.
The picture shows the ventilation holes in a hair dryer.
There are 9 holes in the first circle and 12 holes in the next circle. How does the pattern continue?
Try to figure out an answer before counting the holes in the picture.
Figure out the total number of holes without counting them.