Advent calendar 2020

11 December

Noel has a large pile of cards. Half of them are red, the other half are black. Noel splits the cards into two piles: pile A and pile B.
Two thirds of the cards in pile A are red. Noel then moves 108 red cards from pile A to pile B. After this move, two thirds of the cards in pile B are red.
How many cards did Noel start with?
Note: There was a mistake in the original version of today's puzzle. The number 21 has been replaced with 108.

Show answer


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


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


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