EDIT: Sorry but I didn't know I must have more than 10 Reputation to can use more than 2 images. So I've merged some steps together.
I'll give you the way I use to divide a circle into n parts. You will use Circle Tool , the Tile Clone and the Snapping to do exactly what you want:
1º - Create a Circle and in the Circle Tool Definitions put you n number as the End parameter. 18° degrees for example.
2º - Enable the Snapping and let the options Snap Cusp Nodes and Snap an Item's Rotation Center turned on.
EDIT: If you don't know how to use the Snapping Tool, I suggest you to searh for videos, tutorials, etc, about it. It's very useful. Anyway for now just let equals to the image.
3º- Drag the rotation point (the crosshair that apears when you click twice in a object using the Select And Transform Tool) of the of that piece of circle near to the sharper part of that (where the center of the complete circle will stay) and let the rotation point be attracted by the vertex.
4º - Open the Tile Clone Tool (Edit> Clone>Create Tiled Clone) and do this:
a) In the Shift options, put -100% in the into the Shift X > Per Column field. It will make each clone return to the center of the circle.
b) In the Rotation Options put your n number into the Angle>Per Colunm, in my previous example 18.
c) Choose to Clone by Rows, Colunms. Let 1 for Row and 360 divided by n for Column. Following my example, 360/18 = 20. so I'd put 20 columns.
Finally, push Create and voila!
Notice that each clone is linked to the original piece and you need select all the clones and unlink them in order to edit them, you do this with Edit>Clone>Unlink Clone or Shift+Alt+D
Now you can do what you want with your circle divided into n parts. If you have any problem , let me know.