SOLUTION: using seven distinct straight lines, what is the maximum number of points of intersection?

Question 571515: using seven distinct straight lines, what is the maximum number of points of intersection?
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
Two distinct lines can have at most 1 point of intersection. (They could have none, too).
With seven lines, you can combine them to make 21 different pairs, so 21 is the maximum number of points of intersection.
You can get the number 21 from listing and counting, or remember combinatorics and say

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