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How many lines can you draw using 3 non collinear (not in a single line) points A, B and C on a plane?

Correct Answer: 3

Explanation:

You need two points to draw a line. The order is not important. Line AB is the same as line BA. The problem is to select 2 points out of 3 to draw different lines. If we proceed as we did with permutations, we get the following pairs of points to draw lines.


 


AB , AC


 


BA , BC


 


CA , CB


 


There is a problem: line AB is the same as line BA, same for lines AC and CA and BC and CB.


 


The lines are: AB, BC and AC ; 3 lines only.


 


So in fact we can draw 3 lines and not 6 and that's because in this problem the order of the points A, B and C is not important.


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