So, a friend just challenged you to think of a number between 1 and 1000, huh? Well, here's a simple way to guess the number without guessing random numbers.

Thanks to chooseausername for giving me the game

Thanks to chooseausername for giving me the game

## Step 1: Half of What?

Ok, so your number is big. Like, big as 1000. Well, you don't just guess a random number. You say the number that's half of 1000. Well, how do you figure that out? You shrink the number down, of course! Take the numbers after the second digit down, leaving you with 10. Whats half of 10? 5, of course! After that, add the zeros you took off the 10 to the 5, making it 500.

## Step 2: What If the Number Is Wrong?

Ok, so 500 was wrong. That is to be expected, though. In this case the number is greater, so you have to know what's half of 500 and add it. If the number was lesser, you'd just have to know what's half of 500 and guess from there. So, half of 500 is 250. Then you add 250 to 500, which is 750.

## Step 3: Still Wrong?

Ok, so the number is lower. You can't divide the number by half because it's greater than 500. So, you must go down by 50, making the number 700.

## Step 4: Narrow It Down...

Now, we know the number is greater than 700, but less than 750. So, you guess half of 50 plus 700 which is 725. However, the number is lower, so we guess 5 down, which is 720. The number is still wrong, so we go 10 down, making the number 710. The number was correct, but if it wasn't, it would tell you if it was greater or less, so you would add or subtract 5, and work from there. This time, I only had to guess 5 times, which is a record, but it may take up to 15 tries if you use this method.

Oh, if you want to practice this method, you can play it here.

Thanks for viewing!

Oh, if you want to practice this method, you can play it here.

Thanks for viewing!

i won! beat this:
I'm thinking about a number between 0 and 1000.
Try to guess it !
You said : 500?
My number is lower !
You said : 243?
Congratulations ! You won !
You found my secret number in 1 tries.
Your score is : 1000
(Press Reset to start a new game.)

prove it!
post a picture

will do.

ok. but someone beat that already.
you cant beat him because he got the maximum score already

what if i hack?

1. that will get you disqualified
2. hacking wont help

it helps!
type this into address bar: javascript:alert(random_number);
works in firefox and konqueror.

I'm thinking about a number between 0 and 1000.
Try to guess it !
---> javascript:alert(random_number); <---
---> new window opens: 656 <---
You said : 656?
Congratulations ! You won !
You found my secret number in 0 tries.
Your score is : Infinity
(Press Reset to start a new game.)

game didnt work! it wouldnt display fractions, decimals or exponents.
I'm thinking about a number between 0 and 1000.
Try to guess it !
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?
You said : NaN?

its not supposed to display those things

you mean it wont do fractions, exponents, roots, algebra or basic expressions? lowzy game.

no, its a game, not a homework machine

its not a smart program.

its made with html

i know a neuronal net coded in html!

thus its a dumb program. it should freeze up at math.

its a game

and a dumb one at that

i didnt even make the game! if you're gonna complain, complain to chooseausername

i needed 10 tries. the ****ing number was 559!!!
how should someone guess it???
LOG:
I'm thinking about a number between 0 and 1000.
Try to guess it !
You said : 500?
My number is greater !
You said : 750?
My number is lower !
You said : 700?
My number is lower !
You said : 600?
My number is lower !
You said : 550?
My number is greater !
You said : 560?
My number is lower !
You said : 555?
My number is greater !
You said : 556?
My number is greater !
You said : 557?
My number is greater !
You said : 558?
My number is greater !
You said : 559?
Congratulations ! You won !
You found my secret number in 10 tries.
Your score is : 100

Coolz really left!

I win!

<h2>NEW RECORD HOLDER!</h2><br/>congrats! you have the record forever because that was the maximum possible score!<br/>

Looks like he hacked look at the one of the person who hacked.

Ummm... no. You'll notice it's 500, my first guess. Anyone's first guess.

I just said that because I lost. No hard feelings.

What is your highest score, mine is 200. (on my second try)
You also have it wrong at the third step. You divide the difference of the higher and lower number and add/ subtract it to the last number you guessed and continue doing that until you get the number choosing either the higher or lower when the difference is odd.
Good instructable though, it displays the best way to crack this puzzle.

Where is the link to the game??! Very nice technique, but if would be nice to have a link to the game. Thanks.
-gamer

step 4 has the link

Sorry, I missed it.

Thats...kind of self evident...

Yes =o) <br/>The "half way" method is the best method to make a great score with this game =o)<br/><br/>Like an old and wise philosopher from the ancient times once told to his young apprentice : «<em>My Little Grasshopper, never forget that the middle path is the way to go, because it stands exactly between the path of the Dark Force of the Empire, and the path of the Crazy Force of Sponge-Bob.</em>»<br/>

An old and wise philosopher from ancient named Confusious also once said - He he fishes in another mans well, ends up catching crabs.
Nice instructable :P My record was 9 so far

Reminds me of the binary search in computer science.

It does, although this isn't a completely rigorous binary search. I'm still trying to find a concise way of describing binary search in text- the closest I can find is "guess half way between yoru known upper and lower boundaries, then update your boundaries and guess again". I've got a half-finished Instructable about binary search, actually....

Just so. With a true binary search (guessing halfway between the upper and lower bounds each time), you should be able to find a number between 1 and 1000 in 10 tries, rather than 15.

Haha!

Nice! I never knew that.
I gave it a 4.