# Advent calendar 2018

## 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

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