mscroggs.co.uk
mscroggs.co.uk

subscribe

Advent calendar 2021

7 December

The picture below shows eight regular decagons. In each decagon, a red triangle has been drawn with vertices at three of the vertices of the decagon.
The area of each decagon is 240. What is the total area of all the red triangles?

Show answer

Archive

Show me a random puzzle
 Most recent collections 

Advent calendar 2025

Advent calendar 2024

Advent calendar 2023

Advent calendar 2022


List of all puzzles

Tags

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

Archive

Show me a random puzzle
▼ show ▼
© Matthew Scroggs 2012–2026