+0  
 
-1
115
2
avatar+397 

deleted.

 Oct 26, 2019
edited by sinclairdragon428  Nov 20, 2019
 #2
avatar+125 
+1

So, if each of the 10 circles crosses the other 9 circles twice, that would be 9x10x2. When this is done, you end up counting each pair of circles twice, ie. Circle 1 crosses circle 5 and circle 5 crosses circle 1. So the answer is really 10x9 or 90.

 Oct 26, 2019

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