Guess Who

Overview

Each player has a hidden character. Ask yes-or-no questions to eliminate faces until only one remains. Binary search, for five-year-olds.

This entry is checked against Hasbro's instructions for Guess Who? Classic, item C2124 (©2018).

1. Setup

Two players. Each takes a board of 24 faces, all flipped up. Where each face sits on the board doesn't matter.

Shuffle the 24 mystery cards; each player takes one from the top and puts it in their board's slot, facing themselves. The youngest player goes first.

2. Play

Players alternate asking one yes-or-no question about the other's mystery character: "Does your person wear glasses?"

The opponent must answer truthfully, yes or no, and nothing else.

You then flip down every face that the answer eliminates.

3. Guessing

On your turn you may instead guess the character by name.

The guess replaces your question for that turn.

• Correct — you win.
• Wrong — you lose. The sheet is blunt: "don't take a guess until you're ready—if your guess is wrong, you'll lose the game!"

Letting a wrong guess merely cost a turn is a house rule, and it changes the strategy completely, so agree it before you start.

Championship series: each board has a scorekeeper. Slide it up one per win; first to five wins is the champion.

4. Strategy

The optimal approach is binary search: ask questions that eliminate as close to half the remaining faces as possible.

A question is only as good as its split on your board, so count before you ask. Characters and their features have changed between editions, so a question that halves one set may not halve another.

The sheet suggests, "for an added challenge", not asking whether the character is male or female until the third turn.

With perfect halving, 24 faces resolve in five questions — 2⁵ is 32, comfortably more than 24.

Asking "Is it Bob?" early eliminates one face and wastes a turn. Children do this constantly, which is why they lose.

5. House variants

Not in the official rules; agree them first.

• Two mystery cards each — ask about either.
• Compound questions, such as "glasses or a hat?". The rules only say the question must be answerable yes or no.

Commonly argued

• A wrong name guess loses the game. That's the official rule.
• The youngest player goes first.
• Questions must be answerable yes or no.
• Compound questions need agreeing beforehand.
• The optimal question halves the field, and "is it a man" does not.