Introduction: How to Guess the Mystery Number in Guessing Games

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

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!

Comments

author
tech-king made it!(author)2008-06-30

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.)

author
coolz made it!(author)2008-06-30

prove it! post a picture

author
tech-king made it!(author)2008-06-30

will do.

coolz lost.bmp
author
coolz made it!(author)2008-06-30

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

author
tech-king made it!(author)2008-06-30

what if i hack?

author
coolz made it!(author)2008-06-30

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

author
zimmemic25 made it!(author)2008-10-26

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

author
zimmemic25 made it!(author)2008-10-26

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.)

author
tech-king made it!(author)2008-06-29

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?

author
coolz made it!(author)2008-06-29

its not supposed to display those things

author
tech-king made it!(author)2008-06-30

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

author
coolz made it!(author)2008-06-30

no, its a game, not a homework machine

author
tech-king made it!(author)2008-06-30

its not a smart program.

author
coolz made it!(author)2008-06-30

its made with html

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zimmemic25 made it!(author)2008-10-26

i know a neuronal net coded in html!

author
tech-king made it!(author)2008-06-30

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

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coolz made it!(author)2008-06-30

its a game

author
tech-king made it!(author)2008-07-01

and a dumb one at that

author
coolz made it!(author)2008-07-01

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

author
zimmemic25 made it!(author)2008-10-26

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

author
n8man made it!(author)2008-07-14

Coolz really left!

author
mrmucox made it!(author)2008-06-30

I win!

guess.jpg
author
coolz made it!(author)2008-06-30

NEW RECORD HOLDER!


congrats! you have the record forever because that was the maximum possible score!

author
n8man made it!(author)2008-07-01

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

author
mrmucox made it!(author)2008-07-02

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

author
n8man made it!(author)2008-07-02

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

author
Keith-Kid made it!(author)2008-06-28

Huh???

author
coolz made it!(author)2008-06-28

can you beat my record?

author
n8man made it!(author)2008-06-29

I tied it.

author
coolz made it!(author)2008-06-29

yes, but i have it because i was first

author
n8man made it!(author)2008-06-29

I did mine at 3:43 P.M. PST. When did you do yours?

Coolz game 1.jpgCoolz game 1a copy.jpg
author
coolz made it!(author)2008-06-30

I set the record on the day i made this instructable! i beat you by 2 days!

author
n8man made it!(author)2008-07-01

Ok you win. I agree with you on Skate

author
coolz made it!(author)2008-07-01

nope. this guy called mrmucox got the record...

author
n8man made it!(author)2008-06-29

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.

author
gamer made it!(author)2008-06-29

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

author
coolz made it!(author)2008-06-29

step 4 has the link

author
gamer made it!(author)2008-06-29

Sorry, I missed it.

author
Lithium+Rain made it!(author)2008-06-29

Thats...kind of self evident...

author
chooseausername made it!(author)2008-06-28

Yes =o)
The "half way" method is the best method to make a great score with this game =o)

Like an old and wise philosopher from the ancient times once told to his young apprentice : «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.»

author
NeonLime made it!(author)2008-06-29

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

author
nf119 made it!(author)2008-06-28

Reminds me of the binary search in computer science.

author
PKM made it!(author)2008-06-28

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....

author
snoyes made it!(author)2008-06-28

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.

author
Keith-Kid made it!(author)2008-06-28

Haha!

numbers.bmp
author
Keith-Kid made it!(author)2008-06-28

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

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