12 December

There are 2600 different ways to pick three vertices of a regular 26-sided shape. Sometimes the three vertices you pick form a right angled triangle.
These three vertices form a right angled triangle.
Today's number is the number of different ways to pick three vertices of a regular 26-sided shape so that the three vertices make a right angled triangle.


Show answer


In the diagram, B, A, C, D, E, F, G, H, I, J, K and L are the vertices of a regular dodecagon and B, A, M, N, O and P are the vertices of a regular hexagon.
Show that A, M and E lie on a straight line.

Show answer & extension


Show me a random puzzle
 Most recent collections 

Advent calendar 2020

Advent calendar 2019

Sunday Afternoon Maths LXVII

Coloured weights
Not Roman numerals

Advent calendar 2018

List of all puzzles


partitions sport pascal's triangle numbers scales combinatorics quadrilaterals rugby tiling prime numbers cryptic crossnumbers digits dodecagons calculus addition time palindromes integration parabolas sequences dice triangles surds hexagons routes division graphs irreducible numbers circles number chess arrows folding tube maps digital clocks doubling fractions dates bases advent triangle numbers gerrymandering multiples christmas clocks regular shapes coordinates products angles probabilty menace star numbers cryptic clues proportion sums speed lines coins square roots volume remainders money spheres perfect numbers ave shapes planes the only crossnumber unit fractions crosswords wordplay logic grids people maths factorials complex numbers dominos averages range cards odd numbers polygons cube numbers differentiation floors multiplication mean 2d shapes sum to infinity means 3d shapes perimeter ellipses area rectangles integers shape books games chalkdust crossnumber algebra colouring crossnumber symmetry probability functions quadratics taxicab geometry squares geometry percentages elections balancing factors square numbers chocolate trigonometry crossnumbers median indices


Show me a random puzzle
▼ show ▼
© Matthew Scroggs 2012–2021