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Questions tagged [probability]

A mathematical puzzle whose essential nature involves randomness.

1
vote
3answers
135 views

Jack and Jill went up the Hill to play

A Simple Card Game. This deck of cards has only four cards simply labeled 1, 2, 3, 4. They are placed face down. Jack and Jill take turns to draw a card. You sum up the numbers drawn so far after ...
4
votes
0answers
100 views

Answered it badly…on purpose?

Teacher: You got a 0. Miles Morales: Is that...failed? Teacher: Listen. If you answer all questions on a multiple choice test randomly, you would get a 25%. This means the only way for you to ...
2
votes
3answers
2k views

Should I take the antidote? [closed]

A new disease has been discovered in the world, it is called Blue. Statistically 1:1000 people in the world has it and it makes your whole skin blue in a few weeks after getting the disease but not ...
5
votes
2answers
193 views

SafeCracker #2 - The Mission Continues

Thanks to an alert StackE user, we were able to get the first safe open. Mission Details This next safe is in a former employee's house. He is gone for now, so we have no time to spare. We weren't ...
0
votes
1answer
73 views

Place Your Bets 3 , last of the series

A harder sequence to figure out... What are the next 4 cards, including suits?
1
vote
1answer
51 views

Place Your Bets 2 - In sequence, of course

Your Cards... You have to figure out what the next row of 4 cards will be. There is a pattern in there somewhere, promise. Good Luck
12
votes
12answers
5k views

Coin Game with infinite paradox

Here’s the puzzle/problem: Let’s presume we are best friends. I own the house next to you. I make a gaming proposition along the following lines: You throw a coin over and over again. So long as it ...
4
votes
2answers
228 views

100 prisoners' names in boxes, against smart warden

My question, which I do not know the answer to, concerns the classic 100 prisoners and 100 boxes puzzle, summarized below. The solution to this assumes the names are placed in boxes randomly, and gets ...
42
votes
11answers
8k views

3 doors, three guards, one stone

You are in a room with three doors. You find out that behind two of these doors, the darkest pit of hell is waiting for you to make a mistake. The other door leads to heaven, where you obviously want ...
17
votes
5answers
696 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 ...
15
votes
5answers
2k views

Monty Hall variation

During a train trip I cooked up a semi-autobiographical variation of The Monty Hall problem for people who already know the original. Perhaps it is more of a meta-puzzle than a puzzle, but I hope it ...
5
votes
2answers
810 views

How many cookies does someone need to grab to be certain to obtain a flavor?

I often found this riddle in many exams but I got often confused on how to tackle it. While it involves maths. I wonder if there is a subtle or a more layman method to obtain an answer using common ...
4
votes
1answer
140 views

Minesweeper challenge #5

Coming back to another Minesweeper challenge... I've run into another "unsolvable corner" (corner of a puzzle where there isn't enough information to be 100% certain that any particular square that ...
9
votes
5answers
1k views

How long will my money last at roulette?

I'm at the casino, standing next to a roulette table with a \$10 minimum bet. I want to stay here as long as possible, so I'm going to repeatedly make the minimum bet until I run out of money. I'm ...
5
votes
5answers
3k views

This Website Needs More Cat Pictures?

I love cats! And I love browsing cat pictures! :3 I stumbled on a webpage that shows random cat pictures every time I refresh the page. (For example, this site.) It has a database of $N$ cats ...
1
vote
1answer
81 views

Meeting of 2 Drunk Walkers (Random Walk) [closed]

There are 2 drunk guys who walks according to a Random Walk. Each of them, with equal probability of $ 0.5 $ turns either right or left. They both start at the origin and their turns are synchronized ...
5
votes
1answer
101 views

Puzzle creation problems using unbounded unknown numbers

I occasionally see puzzles that include language like this: You go to buy a specific car, whose fair price we’ll call N. You have absolutely no idea what N is Or this from the same site: Given ...
5
votes
6answers
382 views

A Gambling Problem You Would Love To Have

Let's play a quick gambling game You are going to start by betting a penny, and then I roll a 10-sided die. It is labeled 0 through 9. Whatever you roll, that's what I multiply your bet by and give ...
4
votes
4answers
2k views

A Short Dice Puzzle II

A standard $6$-sided die is put inside a cup. The cup is shaken and put upside-down, hiding the die. You are going to guess what is the number on the top of the die. But, instead of given $6$ ...
4
votes
2answers
166 views

Optimal guess in a game

Suppose that A and B play a strange game. At the beginning of the game A can choose one real number - $x$ - between $0$ and $60$. Each round of the game goes like this: B names random real number $b$ ...
4
votes
0answers
204 views

Will you win the game?

You play a gambling game. On 100 folded pieces of papers are written 100 different values. You cannot see the numbers written on the folded pieces of paper, which are grouped in a pile. You pay 10 ...
10
votes
1answer
3k views

Lost first game – can I still make my mother proud?

I am one of the greatest finger wrestlers of my generation. Only 0.1% of all players are better. When I play against someone who's worse than me, I win 99% of the time. Against someone who's ...
19
votes
8answers
2k views

A Short Dice Puzzle

There are $2$ fair dice: An $11$-sided die, valued from $-5$ to $5$, A $41$-sided die, valued from $-20$ to $20$. You pick one, and I'll take the other one. We roll the dice, and whoever rolls the ...
4
votes
2answers
142 views

Probability in Fighting Tournament in which Contestants consume each other

A tournament has 2 teams of 24 people each of weight 1. Each team sends one person into the pit where they fight until one consumes the other taking on all their weight. The probability that one ...
6
votes
3answers
453 views

Monty's Labyrinth

(A fun combination of two classic puzzles, hope seasoned puzzlers enjoy.) Having escaped through almost all of a labyrinth, you are met by three magical doors. Two of them lead to certain and ...
13
votes
5answers
1k views

Olivia's cookie jars

Olivia loves cookies so much that Dad promises to buy her two cookie jars on one condition: that she only eats one cookie per day. Olivia agrees, and now two black, large cookie jars rest on the ...
10
votes
3answers
630 views

Fight Battle 21

Based off a very, very well-known puzzle The new RPG, Fight Battle 21, is now here! Now with the same three characters as the previous 20 editions! Knight: 6 HP, 60% chance to deal 3 damage Archer: ...
2
votes
2answers
92 views

Risk Appetites - betting percentages

This question is from the September/October issue of the Actuarial Review magazine. Kim and Ann start with an equal amount of money, but they value money very differently. Kim acts to maximize the ...
61
votes
15answers
9k views

2 Monkeys on a computer [closed]

(a) Two monkeys are typing capital letters (A-Z) randomly. The first stops typing when the word COCONUT appears as seven successive letters. The second stops typing when TUNOCOC appears; TUNOCOC is ...
0
votes
1answer
123 views

Minesweeper challenge #4

While solving another Minesweeper puzzle, I ran into yet another unsolvable corner. Well, actually, this time I have two unsolvable corners in the same puzzle. Here's the bottom left corner: ...as ...
1
vote
1answer
99 views

Minesweeper challenge #3

I seem to have run into yet another "unsolvable corner" while playing Minesweeper. The following segment is taken from the bottom right corner of the puzzle. There are 5 mines remaining, and all ...
6
votes
5answers
2k views

Ten targets you need to hit

You are a good sniper and there are 10 targets you need to hit. The chance of hitting any target is the same. Strangely, with your accuracy the chance of getting 8 hits is equal to getting 7 hits in ...
4
votes
2answers
205 views

Minesweeper challenge #2

Again, I seem to have run into another situation where there doesn't seem to be a definitive set of squares to tap to solve a Minesweeper puzzle. What squares should I tap to maximize my chances of ...
3
votes
2answers
192 views

Is there a definite answer to this Minesweeper puzzle? If not, which square has the best chance of being safe?

I was working on solving an Expert puzzle in Minesweeper, but came across a hurdle in this corner (the top left). Is there a definitive solution to the problem? If so, what is it? If not, which ...
-3
votes
1answer
94 views

max possible number of dice throw [closed]

Scott repeatedly rolls a pair of standard six-sided dice and keeps track of the sum of the two numbers rolled each time. So far he has not rolled any sum twice. What is the maximum possible number of ...
6
votes
1answer
194 views

Get 20 points from a target board

A target board consists of four parts, and each part has different numbers on it. You will make at most $10$ shots, and every shot's point will be added to your score. If you get a score of $20$ ...
12
votes
3answers
346 views

Guffin factory regulated heist

I work at a guffin factory. I manufacture guffins and have an unlimited access to guffin storage. I can fit up to 20 guffins in my bag, get them home from the factory and nobody will chase me. You ...
4
votes
6answers
5k views

100 pieces 1 opportunity, choose wisely!

Say you have a cake that is cut into 100 pieces. One of the pieces has a hidden prize. 100 people take turns, each taking a piece in sequence hoping to find the prize. Note: I slightly modified (...
5
votes
3answers
343 views

Probability of Girl or Boy

Suppose that I have a friend whose name is X. X has an elder brother who got married 10 years before. But X being a silly guy has the habit of forgetting things; you can say a “Short time memory loss”....
4
votes
2answers
137 views

3 points on a circle [duplicate]

There is a circle where you put 3 points randomly on it as shown below: What is the chance of these randomly chosen three points passing on an half circle? Reference: Bilim Teknik Dergisi 2018-07
13
votes
4answers
3k views

A dice game, what is the optimal strategy?

Alice was walking on the street when she came across a man playing with a die. She could not help trying to check if the die was loaded and while she was concluding that it wasn't loaded, the man ...
3
votes
0answers
109 views

Variation of Boy/Girl Birth Problem [closed]

Parents keep having children until they have one girl, at which point they stop; and babies are girls with probability 0.49. If we select a child uniformly at random (from the entire population of ...
4
votes
1answer
237 views

How likely is a comeback in basketball?

For this most recent NBA season, ESPN.com has had in-game win probabilities: My question: Say a team gets a big lead and has a 90% chance of winning. What is the probability that at some point ...
10
votes
7answers
461 views

A cooperative guessing game - Guess your order and card

6 players sitting in a circle and each assigned a card among 2 Hearts, 3 Hearts, ..., Ace Hearts (i.e. any of the Hearts cards). Holding her card above his forehead (i.e. Indian Poker fashion), each ...
8
votes
5answers
402 views

Two person game, choosing an integer between 1 and 30?

Suppose two players are playing a game. The first player chose an integer, n st. $n \in \left\{ 1,\ldots ,30\right\}$. The second player picks a different one. After that, a random integer x st. $x \...
1
vote
2answers
228 views

What are the chances on watching the clock? [closed]

This is a relatively straightforward little puzzle, but the answers are somewhat unintuitive or can prompt a new perspective. It might be an interesting little puzzle for a probability teaching ...
5
votes
3answers
495 views

Foolproof double betting

Just made up a problem. Have ideas, but no proof yet – came here for professional help. Tonight an important match of Metagame (box/football/baseball/chess) takes place. Everyone is hyped. Everyone ...
-4
votes
2answers
232 views

Random chord to a circle around a triangle

This puzzle is literally a math textbook question. Its only redeeming feature is that it also happens to be too broad in a surprisingly interesting way. The problem Given the circle $\mathbf O$ ...
32
votes
7answers
5k views

Monty Hall Revisited: Winning Both Goats!

Suppose you're at a game show, knowing the winning strategy for the classic Monty Hall problem. Your turn comes up and you take the stage. You confidently choose door number (?). Just as you are ...
11
votes
2answers
821 views

Expected Number of Tosses Until H,T,T,H

I found a nice little app/game the other day called Probability Puzzles. Apologies to those who, like me, will now obsess until they are all completed. I'm sure there will be many such people on this ...