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Questions tagged [strategy]

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

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13 votes
3 answers
412 views

Keys and Locks Puzzle

Let $a,b,n$ be positive integers in which $a,b\le n$. You are locked in a room, with $n$ distinguishable keys and $n$ distinguishable locks in it. You know that each lock can be unlocked by a unique ...
Culver Kwan's user avatar
  • 5,730
10 votes
2 answers
368 views

The game of 42: 10 cards to make 42

This is a game inspired by other recent questions. It is a 2-player game. The game is played with 10 cards numbered 1 to 10 and 2 positions or stacks. The game starts with all cards in stack 1. The ...
Florian F's user avatar
  • 30.6k
9 votes
2 answers
750 views

Pole, rope, and chasm

You come across a chasm. It's perfectly smooth, 50m deep, and 50m across, and too wide to go around. You have a pole that is 40m long, and as much rope as you need. How do you get across the chasm? ...
Dr Xorile's user avatar
  • 23.6k
20 votes
3 answers
2k views

Winning chance in coins game with fixing

A player plays the following solitaire game. The game consists of as many rounds as are needed to produce a result. They have 20 fair coins, which may in any round be live or fixed; each coin starts ...
Rosie F's user avatar
  • 8,640
2 votes
1 answer
532 views

Is it possible to fill an arbitrarily large hex grid completely given these rules? #2

Based off of this. Lets say you have two players, Red and Blue, that alternate filling an arbitrarily large hexagonal grid of tessellated hexagons with pieces of their color. Hexagons can either be ...
Sny's user avatar
  • 3,165
4 votes
1 answer
508 views

Is it possible to fill an arbitrarily large hex grid completely given these rules?

Lets say you have two players, Red and Blue, that alternate filling an arbitrarily large hexagonal grid of tessellated hexagons with pieces of their color. Hexagons can either be filled or empty. A ...
Alek Erickson's user avatar
23 votes
7 answers
3k views

Two prisoners and twenty marbles

Two prisoners are planning their escape. Their cells are locked with a padlock that must be opened with a 5-digit code (numbers 00000 to 99999). Each prisoner knows the code of the other prisoner's ...
Dmitry Kamenetsky's user avatar
5 votes
4 answers
719 views

The Alien Snails Experiment

Fictional Background Story (The Experiment): Two extremely fast and intelligent alien snails are randomly placed on two different points on an infinite plane, as an experiment by the cruel ruler of ...
Prim3numbah's user avatar
  • 35.1k
12 votes
1 answer
930 views

Anna tries to make triangles from broken sticks

Anna and Boris play a game with a red stick, a white stick and a blue stick, each of which is 1 meter long. Anna starts by breaking the red stick into three pieces. Then Boris breaks the white stick ...
Will Octagon Gibson's user avatar
11 votes
3 answers
2k views

Determine whether the counterfeit coin is heavier or lighter in two weighings on a standard balance

To allow new users to solve this puzzle and earn reputation points, I encourage all users whose reputation is 200 or more to not post an answer until 48 hours after this question is posted. Thank you! ...
Will Octagon Gibson's user avatar
16 votes
2 answers
2k views

Find the heaviest and the second heaviest coins

Each of 32 coins has a different weight. In 35 weighings on a standard balance, find the heaviest and the second heaviest coins. Clarification: Before you start to identify the heaviest and second ...
Will Octagon Gibson's user avatar
17 votes
4 answers
3k views

Magic: the Gathering – Scry-sort

Let me start with a formulation of the problem for people who aren't familiar with Magic: the Gathering. You have a stack of distinct cards face-down. You can apply the following actions arbitrarily ...
A. P.'s user avatar
  • 5,948
5 votes
2 answers
351 views

Making an expression with the numbers 1 to 100 odd (or even)

Anna and Boris play a game with the numbers from 1 to 100 written in order in a row. Anna goes first, and turns alternate thereafter. In each move, a player puts one of the operation signs +, − and × ...
Will Octagon Gibson's user avatar
2 votes
0 answers
153 views

Dumb robot on chessboard [duplicate]

A robot is placed on the square A1 of a standard chessboard and has to reach H8. It understands orders Up, Down, Left, Right. On some squares, there might be a cement block; is such a case, the robot ...
kaksi's user avatar
  • 189
1 vote
0 answers
60 views

Change all eight numbers to 1 [duplicate]

A solitaire game starts with eight numbers arranged in a circle. Each is either 1 or −1, and the choice is arbitrary. In each move, one can multiply any three adjacent numbers by −1. Prove that one ...
Will Octagon Gibson's user avatar
6 votes
2 answers
198 views

River crossing cats and dogs

A farmer and his $n$ cats and $m$ dogs are on one side of a river. There is a boat that can carry the farmer and at most $k$ animals at once. The boat doesn't move without a person operating it. The ...
Bubbler's user avatar
  • 14.7k
3 votes
3 answers
874 views

You have magic, but sometimes the spell backfires: how to win regardless? [closed]

This one is convoluted, and I’m not sure if there actually is an answer. For a character in a story. You have magic and want to rig a sporting event. However sometimes the spell will backfire. The ...
rclev's user avatar
  • 141
8 votes
2 answers
529 views

Seven genuine and two fake coins

Seven genuine coins have the same weight. Two counterfeit coins also have the same weight. A counterfeit coin is heavier than a genuine coin. Identify the fake coins using a standard balance at most ...
Will Octagon Gibson's user avatar
28 votes
4 answers
5k views

Can you beat random?

It is known that one cannot beat a truly random player in Rock Paper Scissors. Here you will play a variant of the game. In this variant you are not allowed to play the same shape twice in a row. So ...
Dmitry Kamenetsky's user avatar
2 votes
2 answers
365 views

Press The Grue Button

[This puzzle is inspired by the webpage https://apparenthorizons.com/2017/10/12/the-grue-problem-and-deep-learning/] 55 workers have got a chance to double their pay, as said by their boss. So, the ...
3-1-4-One-Five's user avatar
4 votes
1 answer
369 views

The Monty Hall loot box

Everyone sufficiently competent in probability knows that in The Monty Hall problem as most commonly presented, switching doors wins you the car $\frac23$ of the time. I have come up with this ...
Parcly Taxel's user avatar
  • 7,720
6 votes
2 answers
1k views

Two Trains, One Track

Two trains are heading towards each other on a track. One train is blue, the other is green. Each train has a locomotive hauling nine wagons. Each locomotive is 10 meters long, and each wagon is also ...
Gec's user avatar
  • 185
1 vote
1 answer
345 views

SEVEN-COUNTERS GAME

This simple puzzle is from the 1908 book “A Scrap-Book of Elementary Mathematics” by William F. White. Required to place seven counters on seven of the eight spots in conformity to the following rule:...
Will Octagon Gibson's user avatar
33 votes
3 answers
2k views

Sliding crosses in a 5x5 grid

Well you probably already knew that this was coming after the last two puzzles :) I believe this is the most beautiful one. You are given a 5x5 grid with 3 crosses as shown below. Each turn, you can ...
Dmitry Kamenetsky's user avatar
12 votes
4 answers
998 views

Sliding crosses in a 4x4 grid

You are given a 4x4 grid with 3 crosses as shown below. Each turn, you can select a cross and slide it along horizontally or vertically. It will continue sliding until it hits another cross or a wall. ...
Dmitry Kamenetsky's user avatar
8 votes
3 answers
474 views

Sliding crosses in a 3x3 grid

You are given a 3x3 grid with 3 crosses as shown below. Each turn, you can select a cross and slide it along horizontally or vertically. It will continue sliding until it hits another cross or a wall. ...
Dmitry Kamenetsky's user avatar
9 votes
5 answers
421 views

1000 Batches, 1 Poisoned, 4 Mice, Minimized Costs

You work at a pill factory that recently produced $1000$ batches, each with ample samples. Your boss has just discovered that exactly one batch is entirely poisoned, and just one pill from it will ...
Pumbaa's user avatar
  • 938
9 votes
5 answers
605 views

Minimum K for detecting fake pearls in one weighing

There are 10 boxes, each with the same number of pearls (represented by K). Genuine pearls weigh 30g each, while fake pearls weigh 29g each. Each box is either all genuine or all fake, and any number ...
Pumbaa's user avatar
  • 938
1 vote
1 answer
199 views

Two Sheriffs and Eavesdroppers - 3

“The Two Sheriffs” puzzle was already discussed here. This puzzle has only one difference: we have six suspects instead of eight. Two sheriffs in neighboring towns are on the track of a killer, in a ...
mathlander's user avatar
  • 1,261
12 votes
1 answer
2k views

Poison ivy chess: Can the king get to safety?

The king is on a chessboard filled with poison ivy bushes. Can the king get to safety? Details: The king is initially located at the top left-hand corner square of the chessboard. The finite ...
Will Octagon Gibson's user avatar
18 votes
1 answer
597 views

Game of the glasses on the windowsill

The windowsill above the sink is where my wife and I place our dirty wine glasses. And while both of us love each other, neither of us love loading the dishwasher. As a result, these dirty glasses ...
Feryll's user avatar
  • 2,389
0 votes
2 answers
232 views

Wounded Soldiers/Crossing a Bridge Puzzle - checking a solution

I am working on a Prolog university assignment, where we have to determine what the shortest time is for 4 wounded soldiers to cross a bridge to safety. This seems to be a variation of the more common ...
Gerhardus Carinus's user avatar
1 vote
1 answer
291 views

Fox and rabbit on a circle

There are five holes in a line. One of them is occupied by a rabbit. Each night, the rabbit moves to a neighboring hole, either to the left or to the right. Each morning, a fox gets to inspect a hole ...
user85065's user avatar
5 votes
1 answer
855 views

How did she do that?

The King wants to test his 2 very smart advisors Sadin and Lena. In the courtyard he sets up 4 closed wooden boxes on a table. All are the exact same size. In front of each box there is a name plate. ...
RogerA's user avatar
  • 6,607
4 votes
2 answers
473 views

Think in a Odd way

You have been captured for the crime of making a rude comment on Puzzling Stack Exchange and sent to Puzzlcatraz, a special prison for perfectly logical logicians. The warden is fair and decides to ...
Box Enthusiast's user avatar
-2 votes
1 answer
190 views

The Island of Arbitrary Puzzles [closed]

One day, an eccentric billionaire who’s obsessed with puzzles decides that he needs to open a theme park based on them. After throwing money at the problem for a few years, he finally finishes. ...
Box Enthusiast's user avatar
5 votes
2 answers
1k views

Shortest time to cook burgers

Attribution: I remember seeing this type of question some time ago but don't remember from where. So I have redesigned the question. Hope that is OK. You have 5 burger patties to grill. Each side ...
RogerA's user avatar
  • 6,607
6 votes
4 answers
760 views

How to Divide 1,987 Gold Coins Among 40 Pirates?

There are 40 pirates, designated as P1, P2, ...... P40, respectively. They aim to divide 1,987 gold coins using a two-stage division scheme: In the first stage, P1 initially splits all the coins into ...
Pumbaa's user avatar
  • 938
14 votes
2 answers
1k views

Drowning Squirrel

On a super foggy day, a squirrel falls from a tree into a swimming pool. Due to fog, it cannot see any bank of the pool, unless it touches the bank. It is aware that the swimming pool is in the shape ...
thisIs4d's user avatar
  • 1,083
-4 votes
2 answers
220 views

Catch the mouse (Easy)

A mouse is at the center of a square. There are 4 cats each on the mid-points of different sides of the square. Mouse is looking to escape to any corner of the square. Mouse and cats have the same ...
thisIs4d's user avatar
  • 1,083
4 votes
2 answers
341 views

A safe with 4 locks

You are trying to open a safe. There are 4 locks and 4 keys (red, green, blue and yellow). When you insert the keys into the locks, the safe will make k beeps, where k is the number of keys that are ...
Dmitry Kamenetsky's user avatar
6 votes
2 answers
712 views

Attacking Hyenas

$N$ Hyenas are standing on a plane region in a forest. At $t=-1$, they see dead meat nearby. Being selfish, at $t=0$, each Hyena attacks the Hyena which is closest to it. All pairwise distances ...
thisIs4d's user avatar
  • 1,083
10 votes
1 answer
302 views

Equilibrium of differences

There is a subtraction equation written on the board, with three digits minus three digits, and the first digits both fixed. Alice and Bob need to fill in the remaining 4 digits (A~D below) using 4 ...
Pumbaa's user avatar
  • 938
-1 votes
1 answer
122 views

100 prisoners and a secret number (potential solution) [closed]

Please ignore this question I came across the brilliant 100 prisoners and a secret number and have a potential solution which I can't find any flaw with. Can you please let me know what I'm missing. ...
Legend_Killer's user avatar
7 votes
5 answers
937 views

Colorblind Mastermind

This puzzle is part of the Monthly Topic Challenge #7: Board games. Inspired by the incident, I created a variant of Mastermind, although it wasn't actually intended for colorblind people. The main ...
Scratch---Cat's user avatar
2 votes
2 answers
423 views

A bit complicated 20 card games v2

this is follow up question of A bit complicated 20 card games. As the person who determines the order of the cards without changing the numbers on them, you want to make it more difficult for the ...
Oray's user avatar
  • 30.3k
3 votes
1 answer
353 views

A bit complicated 20 card games

In the game of 20-card games, the objective is to select a card or pass on it at every turn, with the goal of maximizing the sum of the numbers on the chosen cards. You have knowledge of the numbers ...
Oray's user avatar
  • 30.3k
2 votes
1 answer
249 views

Good and bad numbers of remaining mines

You've been tasked with finishing solving this Minesweeper board: "How many mines remain?", you ask. "I'm just choosing that now, actually. Tell you what: I was going to consider every ...
Joseph Sible-Reinstate Monica's user avatar
-1 votes
1 answer
167 views

Coin weighing - heaviest or lightest

I have 6 coins Each coin has different weight I can weigh as many coins at a time on a scale (for example I can weigh 3 vs 2) I want to determine which coin is second heaviest or second lightest in ...
popcorn's user avatar
  • 263
3 votes
2 answers
287 views

Ball weighing - second heaviest

Let's say we have 6 balls, where all of them have different weight. Find and describe the least weighings you need on scales to find second lightest ball and second heaviest ball.
popcorn's user avatar
  • 263

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