mscroggs.co.uk
mscroggs.co.uk

subscribe

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

Archive

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

Tags

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

Archive

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