Quite easy really. Draw a circle then a line from the centre to the top intersection of the circle.
Now draw just ONE of the teeth and centre this on the top of the circle
Type ARRAY then enter
Select polar array (circular)
Pick the centre point (of circle)
Now select the object to array and right click (in this case the single tooth)
If you now fill in the number of teeth required it will now place then aroung the outside of the circle both the same and equally spaced.
You may have to play around with the amount etc... to get it to work perfect.
Hope this helps