Henry Ernest Dudeney/Modern Puzzles/101 - Twenty Questions

Modern Puzzles by Henry Ernest Dudeney: $101$

Twenty Questions

I am reminded of an interesting old game I used to play as a bachelor.

Somebody thinks of an object -- say Big Ben, or ...

You have then to discover the object, by putting not more than $20$ questions, each of which must be answered by "yes" or "no".

You have to word your questions discreetly, because if you ask, for example,

"Is it animal, vegetable or mineral?" you might get the unsatisfactory answer "Yes," and so waste a question.

We found that the expert rarely failed to get an exact solution, and I have known some most remarkably difficult cases solved by the twenty questions.

A novel limitation of the game is suggested to me, which will call for some ingenuity, and the puzzle will doubtless be attacked in various ways by different persons.

It is simply this.

I think of a number containing six figures.

Can you discover what it is by putting to me twenty questions,

each of which can only be answered by "yes" or "no"?

After the twentieth question you must give the number.

Sources

• 1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Arithmetical and Algebraical Problems: Various Arithmetical and Algebraical Problems: $101$. -- Twenty Questions
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Arithmetical and Algebraical Problems: Miscellaneous Puzzles: $182$. Twenty Questions