# Puzzles

## Archive

Show me a random puzzle**Most recent collections**

#### Sunday Afternoon Maths LXVII

Coloured weightsNot Roman numerals

#### Advent calendar 2018

#### Sunday Afternoon Maths LXVI

Cryptic crossnumber #2#### Sunday Afternoon Maths LXV

Cryptic crossnumber #1Breaking Chocolate

Square and cube endings

List of all puzzles

## Tags

differentiation percentages perimeter coordinates averages cryptic crossnumbers 3d shapes palindromes sums multiplication routes triangles clocks chess balancing digits sequences proportion parabolas division rectangles dodecagons folding tube maps quadratics angles ave crosswords unit fractions squares surds speed christmas polygons 2d shapes dates star numbers number money numbers triangle numbers perfect numbers shape probabilty hexagons functions square numbers taxicab geometry prime numbers people maths square roots cube numbers logic rugby graphs trigonometry crossnumbers irreducible numbers scales multiples regular shapes calculus pascal's triangle mean area cards means cryptic clues geometry integers lines factorials remainders addition fractions sport indices advent doubling bases complex numbers algebra factors sum to infinity odd numbers games chocolate planes arrows menace floors time wordplay partitions dice spheres coins shapes ellipses circles chalkdust crossnumber volume grids books probability integration colouring symmetry## 12 December

There are 2600 different ways to pick three vertices of a regular 26-sided shape. Sometime the three vertices you pick 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.

## Dodexagon

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.