Guess the Number

What You Need

• Nothing. Two people and a range of numbers.
• Paper helps if you play the limited-guess version and want to keep score.

Setup

1. Agree on a range. 1 to 100 is the standard. 1 to 10 is fine for small kids. 1 to 1,000 for a longer hunt.
2. Decide who picks first. The picker chooses a whole number in the range and keeps it secret. Write it down so nobody can change it later.

How a Round Works

1. The guesser says a number.
2. The picker answers "higher," "lower," or "that's it."
3. Repeat until the guesser hits the number.
4. Count the guesses. The correct guess counts as one.
5. Swap roles and play again with a new number.

Scoring

Your score for a round is the number of guesses you needed. Lower is better. Play an even number of rounds so each player picks and guesses the same number of times. Add up your guesses. Lowest total wins.

Winning

Whoever needs fewer total guesses across the same number of rounds wins the match. Best of 6 rounds, 3 guessing each, is a good length. It takes about 10 minutes.

Two-Player Notes

The game is two-player by nature. One picks, one hunts. The only fairness issue is the swap. Never let the same player guess twice in a row. Swap after every round and use the same range for both players.

The Halving Trick

Always guess the middle of what is left. On 1 to 100, guess 50. If the answer is "higher," the range is 51 to 100, so guess 75. If "lower," the range is 1 to 49, so guess 25. Each guess cuts the field in half. Seven guesses always finds a number from 1 to 100. Ten guesses covers 1 to 1,000. Twenty covers 1 to 1,000,000. If you play this way every time, the game is solved and the picker cannot beat you. That is why the variations below exist.

Strategy Tips

• As the picker, choose numbers that punish sloppy guessers. 37, 63, 87. A guesser who skips the halving trick tends to hop between round numbers, so odd numbers far from 50 take them longer.
• Do not pick 50, 25, or 75. Those are the first three guesses of anyone who knows the trick.
• As the guesser, say the halfway point out loud before you decide. It stops you from wasting a guess on a hunch.
• Keep the range in your head as two numbers, low and high. Update both after every answer.

Variations

• Limited guesses. The guesser gets a fixed number of tries, usually 7 for 1 to 100 or 5 for 1 to 30. Miss and the picker wins the round. Seven on 1 to 100 is always enough if you halve, so use 6 to give the picker a real chance.
• Hot and cold. The picker says "hot" when the guess is within 5, "warm" within 15, and "cold" otherwise. No higher or lower. This kills the halving trick and turns the game into a search.
• Bigger ranges. 1 to 1,000 takes 10 guesses with the trick. It is a good way to teach kids why halving works.
• Two-way race. Both players pick a number at the same time and take turns guessing each other's. First to hit wins. A picker who answers slowly is stalling. Count to 3.
• Two numbers. The picker chooses two numbers. The guesser must find both. Higher and lower refer to the closer one. Hard.