A bag contains \(m\) blue and \(n\) yellow marbles. One marble is selected at random from the bag and its colour is noted. It is then returned to the bag along with \(k\) other marbles of the same colour. A second marble is now selected at random from the bag. What is the probability that the second marble is blue?

Show answer & extension

If you enjoyed this puzzle, check out Sunday Afternoon Maths XXXV,
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


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


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