Triangles across two lines
Four points lie on one straight line and three more points lie on a second, parallel line (seven points in all; no other three are collinear). How many triangles have all three vertices among these points?
Show hints (2)+
- Count all triples of points, then subtract the collinear ones (they aren't triangles).
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Answer
Reveal answer →Final answer
30
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Asked at: Timed Mental-Math & Sequences, Game-Based Aptitude