Henry Ernest Dudeney/Puzzles and Curious Problems/240 - Counting the Triangles
Jump to navigation
Jump to search
Puzzles and Curious Problems by Henry Ernest Dudeney: $240$
- Counting the Triangles
- Draw a pentagon, and connect each point with every other point with straight lines, as in the diagram.
- How many different triangles are contained in this figure?
- To make it quite clear, $AFB$, $AGB$, $ACB$, $BFG$, $BFC$, and $BGC$ are six such triangles.
- It is not a difficult count if you proceed with some method,
- but otherwise you are likely to drop triangles or include some more than once.
Click here for solution
Sources
- 1932: Henry Ernest Dudeney: Puzzles and Curious Problems ... (previous) ... (next): Geometrical Problems: Various Geometrical Puzzles: $240$. -- Counting the Triangles
- 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Geometrical Problems: Triangle, Square & Other Polygon Puzzles: $277$. Counting the Triangles