The blue-eyed sisters

If you happen to meet two of the Jones sister (two sisters chosen at random from all the Jones sisters), it is exactly an even-money bet that both will be blue-eyed. What is your best guess of the total number of Jones sisters?

Show answer & extension

If you enjoyed this puzzle, check out Sunday Afternoon Maths XXXII,
puzzles about probability, or a random puzzle.


Show me a random puzzle
 Most recent collections 

Advent calendar 2019

Sunday Afternoon Maths LXVII

Coloured weights
Not Roman numerals

Advent calendar 2018

Sunday Afternoon Maths LXVI

Cryptic crossnumber #2

List of all puzzles


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


Show me a random puzzle
▼ show ▼
© Matthew Scroggs 2012–2020