The History of Odd-One-Out Puzzles
Finding the one that does not fit is a classic exercise in school books and thinking tests - it trains sorting things by their features.
Sorting and Grouping
Putting things into groups by a shared feature is one of the first kinds of thinking children practise: animals here, tools there, round things and angular things. Picture books, kindergarten games and workbooks have long asked children to name the one thing that does not belong to its group.
One Clear Answer
In a badly made puzzle several cards could be called the odd one, each for a different reason, and children rightly object. In a good puzzle the rule is hidden but the answer is certain: only one card is different from all the others in some feature.
How PaperGames Makes Each Round
Group rounds take cards from one group of the twenty drawings and one from another group; shape rounds build cards from shape, filling and number. Before a round is used, the program checks that exactly one card could be called the odd one out, so there is one right answer.