# Advent calendar 2018

## Archive

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#### 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

complex numbers addition spheres circles algebra shape planes squares probability cryptic clues quadratics books multiples colouring hexagons square numbers taxicab geometry division advent crossnumbers arrows proportion volume sums crosswords odd numbers percentages dates factors balancing lines sport bases cube numbers rugby dodecagons graphs number regular shapes cards routes fractions time star numbers 3d shapes sum to infinity people maths rectangles mean floors probabilty money shapes logic square roots games chalkdust crossnumber symmetry chocolate indices surds coins scales grids ave functions integration menace partitions dice christmas parabolas polygons clocks wordplay 2d shapes geometry chess differentiation integers multiplication calculus irreducible numbers folding tube maps means perfect numbers triangles perimeter triangle numbers factorials speed angles digits doubling ellipses cryptic crossnumbers sequences numbers pascal's triangle coordinates prime numbers trigonometry averages area remainders unit fractions palindromes## 7 December

There is a row of 1000 closed lockers numbered from 1 to 1000 (inclusive). Near the lockers, there is a bucket containing the numbers 1 to 1000 (inclusive) written on scraps of paper.

1000 people then each do the following:

- Pick a number from the bucket (and don't put it back).
- Walk along the row of lockers and change the state (open them if they're closed and close them if they're open) of all the lockers that are multiples of the number they picked (including the number they picked).

Today's number is the number of lockers that will be closed at the end of this process.