Questions tagged [strategy]

A puzzle whose solution is a methodological plan of action for realizing a specific goal.

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7answers
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23 Clones and Two Lightbulbs

Rise and shine, Mister Bond. James awoke to find himself yet again imprisoned by an evil genius. At least, that's what he presumed. He was alone in a room with a strange device: it consisted of a ...
27
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10answers
3k views

One prize, infinitely many choices

Having reached the final stage of a game show, you face an endless row of doors labelled $1$, $2$, $3$, ... The game show host has selected a whole dollar amount, and has put this exact amount as a ...
26
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3answers
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Finding digits that sum to 15

Rand and Rubio are playing a game in which they each take turns to pick a digit between 1 and 9, without replacement (i.e. all digits chosen are distinct). If one of them manages to get three digits ...
26
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5answers
5k views

You trolls, get out of my party!

You have invited $2017$ of your acquaintances to a party. But after they all arrive, you come to know from a reliable source that each of your guests is either a troll or a true friend. You don't know ...
25
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4answers
2k views

Black wants to go first!

Billy and Matthew decide to play a game of Chess. They live far away, so they decide to do it online. Matthew wants to play first, but the game randomly gave him the color black (who goes second.) ...
25
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4answers
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Lions and Zebras on a Chess Board

The black knight is our lion chasing 8 white bishop zebras which can't capture. Can the zebras evade the lion forever, if team zebra positions all the pieces and has the first turn? Rules: The game ...
25
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3answers
1k views

The lion and the zebras II: The lion with millimeter-long claws

This is a variant of this excellent question. The rules of the lion-zebra hunger games are exactly the same: The lion plays a deadly game against a group of 100 zebras that takes place in the ...
23
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3answers
2k views

Gambling in a rigged casino

A well-known crooked casino is offering the following bet with a pair of (identically looking and indistinguishable) dice that both show the numbers $1,2,3,4,5,6$ on their faces. The first die ...
22
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2answers
3k views

The Dwarves' Test

One day, the chief of the dwarves decided he wanted to test his tribe. So that night, he told the dwarves that he would paint on each dwarf's back a dot colored either red or blue. Each dwarf will ...
21
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4answers
6k views

Picking up stones

Here is puzzle that was lifted from an old essay of mine, that was adapted from a puzzle in an old puzzle book. The great shah has invited a young boy into his palace as a student. While he is not ...
21
votes
2answers
2k views

Rook game on chessboard

A rook stands in the lower left corner of an $m\times n$ chessboard. Alice and Bob alternately move the rook (horizontally or vertically, through any number of squares). As the rook moves, it leaves a ...
21
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6answers
2k views

A game with 52 cards

Alice and Bob play the following game with two (identical) standard decks of $52$ cards. First Alice secretly arranges one deck of $52$ cards in a long row on the table. All cards are face-down, and ...
21
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5answers
1k views

Detectives vs Nelson: The Chessboard Serial Killer

This is about Nelson, a serial killer who, after each murder, leaves a chess diagram in the scene of the crime. These chessboards give the detectives the opportunity to decipher where, how and when ...
21
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4answers
2k views

Even and Odd game

You are playing a game with your friend on a $7$x$7$ grid board. In every turn, you begin by putting a $0$ (zero) on any empty square on the board, and then your friend puts a $1$ (one) on a ...
20
votes
3answers
5k views

The lake monster

You are on a rowboat in the middle of a large, perfectly circular lake. On the perimeter of the lake is a monster who wants to eat you, but fortunately, he can't swim. He can run (along the perimeter)...
20
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5answers
4k views

Battleship- Best Next Move

Mason likes the game Battleship, but he doesn't win much. However, Sherry, his opponent, is so confident in her skill and luck that she has agreed to let Mason have his five friends help him. Sherry'...
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votes
4answers
1k views

Strategy to beat the casino over the long haul

$A$ and $B$ are attempting to beat the casino again, and the rules are the same: Each round, $A$, $B$, and the casino simultaneously decide to show a $0$ or a $1$. If all three numbers match, $A$ ...
20
votes
2answers
1k views

Titanicker Tic-Tac-Toe

This is something of a follow-on to Hugh Meyer's enjoyable "Titanic Tic-Tac-Toe." Fortunately, our intrepid heroes Xavier and Oliver have wrested away a bit of wreckage that some fellow named Jack was ...
19
votes
11answers
45k views

6 Tries to Guess a Number Between 1-100

After every time you guess, you're told if you're right, too high, or too low. Is there a strategy you can use to guarantee you'll get it on your 6th attempt (or lower)? I know a strategy to get it ...
19
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5answers
4k views

Can you open the door or die? v2

This is the follow up question to my previous question You wake up and find yourself in a very strange room with a single door. You find a note on the ground surrounded by lots of cards: ...
19
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5answers
3k views

Dwarfs over bridge problem

300 dwarfs go over a bridge in the middle of the night. The bridge is rickety and manages at most two dwarfs at a time. With them is a lantern that they must provide at each transition. Dwarfs need ...
19
votes
4answers
2k views

Obtain the “Master of stones” title

Note : the mechanisms described in this puzzle are related to those found in this question. This is a game of 2 players. Each player can pick up 1, 2, or 3 coins in any pile (copper , silver , gold) ...
18
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4answers
3k views

A Tic-Tac-Toe type game

I found this interesting game with no name: You have a 1x11 grid, like this. The way you play is similar to Tic-Tac-Toe (aka Noughts and Crosses). Players take turns to place Xs and Os on the grid, ...
18
votes
3answers
7k views

Knight on a 5 by 5 board

Alice and Bob play a game with a $5\times 5$ chessboard, and a chess knight. Alice begins by placing the knight somewhere on the board. Then, starting with Bob, the players alternate moving the knight ...
18
votes
6answers
3k views

Guess five binary digits!

Person A thinks of a 5 digit binary number. Person B tries to guess the number. B can guess a 5 digit binary number and A will respond with the number of correct digits (digits in the right place). ...
18
votes
10answers
4k views

How to get voters to vote against themselves [closed]

On an island far away, there are people. They have an ancient law which states that anyone can propose a new law. However, new laws must be voted upon immediately after proposal (i.e there is no time ...
18
votes
8answers
2k views

30 fake coins out of 99 coins

You are given 99 coins which consists of 30 fake ones. You also have a digital balance scale with perfect precision that shows how much difference between weighs you put on. For example, if you put 10 ...
18
votes
3answers
6k views

Can you Turn MI to MU?

Using the letters M, I, and U, which can be used to create words. Can you turn MI into MU using in each step one of the following rules: Insert a U to the end of a word ending in I. e.g: MI becomes ...
18
votes
1answer
1k views

The Delayed Guessing Game

This is a similar but harder version of 6 Tries to Guess a Number Between 1-100. You friend gives you $n$ tries to guess an integer $x$, $1\le x\le 100$. Your guesses must be of the following type: ...
17
votes
10answers
1k views

Communicating Information about Cards

Seven cards, numbered $1,2,3,4,5,6,7$, are distributed randomly among three people: Rand gets one of them, Deusovi gets three of them, and Gareth gets three of them. All three know what the seven ...
17
votes
6answers
4k views

Guess my number! Pay for the answer!

Alice and Bob play the following number guessing game. In the beginning, Alice picks a secret number from the range $1,2,3,\ldots,144$. Then Bob is allowed to ask a sequence of questions. In every ...
17
votes
4answers
2k views

Two prisoners and the prison ward

Two prisoners are imprisoned at opposite ends of the prison. They cannot meet, nor exchange any kind of information. However, one day they are brought together by the ward who tells them: "I shall ...
17
votes
5answers
698 views

Blindfold Bingo

Congratulations, you have been selected from among the audience to compete in the fabulous Blindfold Bingo challenge! (cue annoying, yet catchy theme music.) Here you see our perfectly ordinary Bingo ...
17
votes
2answers
466 views

What is the optimal strategy for this triangular board game?

I saw a board game somewhere and I want to know the optimal strategy for it. The game is played on a triangular board with 21 slots: The two players, red and blue, take turns to put numbered circles ...
16
votes
10answers
3k views

5 people each have 5 equal cards

A competent logician is playing cards with four of his friends, so that there are a total of 5 people sat around the table. Each player has the same 5 cards, showing A, 2, 3, 4, and 5 (Ace being low). ...
16
votes
2answers
2k views

Game of Drones - Zap it!

Your programmable drone is pitted against another drone in a rectangular 3D arena measuring 40 meters long, 40 meters wide and 20 meters high. You have equipped your drone with a laser gun that will ...
16
votes
4answers
939 views

Fifty-two genuine and two fake coins

In the country Borgonia, there are only two types of coins: genuine ones and fake ones. All genuine coins have the same weight, and all fake coins have the same weight. The weight of a genuine coin is ...
16
votes
1answer
2k views

A game with 330 pebbles

Anastasia and Barnabas play a game that starts with $330$ pebbles in a bowl. The game consists of two phases. The first phase looks as follows: First Anastasia announces an integer $A$ with $2\le A\...
16
votes
1answer
1k views

The Bucket of Sand

Disclaimer: This riddle MAY have been given elsewhere. I heard this one a few months ago from a friend, and I have no idea what his source was. You're in a room, since that's your job. Your singular ...
16
votes
1answer
581 views

Let's make Mango Orange Apple Juice!

Annie recently took a temp job at the famous juice shop, All About Juice. As is the case with most juice shops, creative mixtures are the norm, but the store's most famous product is still its ...
16
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2answers
1k views

Tic-Tac-Toe variant

To help people think this out, I've made a web game with increasingly difficult cpu players to allow brainstorming and testing strategies: cpu player, easiest (version 1 - at least 5-in-a-row is ...
16
votes
2answers
346 views

If you have 3 random numbers between 1 and 27 can guess the fourth?

Problem: Ashley and Ivan want to impress their friends and come up with a magic trick: One of their classmates comes up with 4 unique random numbers between 1 and 27 and tells them to Ivan. Ivan ...
15
votes
9answers
4k views

Solitaire Chess

A friend of mine got me Solitaire Chess for Christmas years ago. I set up the board below. Is it possible to solve it? If so, what is the solution? (No programs allowed- Use only your brain.) Rules: ...
15
votes
5answers
2k views

Two genuine and two fake coins

In the country Argonia, there are only two types of coins: genuine ones and fake ones. All genuine coins have the same weight, and all fake coins have the same weight. The weight of a genuine coin is ...
15
votes
9answers
3k views

A search game with 2016 numbers

Alice secretly chooses $2016$ integers $x_1,x_2,\ldots,x_{2016}$. Among these $2016$ integers there are $2015$ that all have the same value, and there is only one number $x_k$ that takes a different ...
15
votes
6answers
2k views

The punctual worker and the stingy boss

Tom works with a stingy boss that will deduct from his salary for every minute that he's late for work. Unfortunately, Tom has to pass by the boss's office on the way to his cubicle. Being a lazy ...
15
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10answers
2k views

The barbarian king [duplicate]

A barbarian king wants his tribe to have more men than women, because men can fight and women cannot. to achieve this, he introduces the following law: Each couple has to produce babies until they ...
15
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9answers
2k views

The Trickster's Game

While walking around the streets of your local city, you encounter a strange woman sitting atop a gigantic pile of dollar coins. "Would you like to play a game?" she asks. Intrigued by the strange ...
15
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3answers
2k views

Sink the Submarine

There is submarine somewhere on the number line. Initially (say, at midnight), it is at position $A$, and is moving $B$ units per hour to the right, where $A$ and $B$ are both integers; both $A$ and $...
15
votes
2answers
2k views

10 prisoners and 10 lists of numbers [duplicate]

10 prisoners are held captive by a cruel warden. One day he gathers them in the prison hall and tells them about a new game he wants to play: "Tomorrow, I will assign each one of you a random ...