A Dice Bet

Logic Level 2

Mary and John roll seven fair, standard dice (like those seen above). If all rolls are the same, Mary wins. If all rolls are different, John wins. They keep rolling all of the dice until someone wins. Who is more likely to win?


Inspired by a Murderous Maths book.
Both have the same odds Mary John Not enough information

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28 solutions

Pola Forest
Mar 19, 2014

The point is to read carefully. There are SEVEN dice, and a dice has only 6 sides. Therefore, even thought it will take Mary a long time, she is sure to win, because it's IMPOSSIBLE to throw all the seven dice differently.

Ahhh!! Thats Brilliant! I feel like a fool now :P

Jayant Kumar - 7 years, 2 months ago

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me too

Vamsi Yerraguravagari - 7 years, 2 months ago

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me too

shiva raj - 7 years, 2 months ago

But the question doesn't mention how many tries they take.

Abhay Gupta - 7 years, 2 months ago

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trials doesn't matter you indefinitely John will never win

Harendra Kumar - 7 years, 2 months ago

Number of trials is trivial here.

Ankit Tripathi - 7 years, 2 months ago

its a game-theory question... they have infinite tries/throws.

Ashish Mishra - 7 years, 2 months ago

it is not dependent on how many tries they will take in 7 dice at last one number will come twice if we take that each die shows a different number

you're all smarter than i am

Josh Silverman Staff - 7 years, 2 months ago

Ditto!!

Tanya Gupta - 7 years, 2 months ago

yes Pola Forest is Perfectly right seven dice having six side can never show seven seven different number.

razi ur rehman - 7 years, 2 months ago

Pola is absolutely right. There is no possibility of John winning because of the fact that dice has six sides. and even if john gets different sides the seventh in all cases will have one similar side surely.

Jyoti Verma - 7 years, 2 months ago

that's perfect problem and perfect solution

Harendra Kumar - 7 years, 2 months ago

I wanna kill myself.

Vaibhav Manocha - 7 years, 2 months ago

exactly........the pigeonhole principle is as mathematical it gets.........if u dont want to rely on pure logic....

D biswas - 7 years, 2 months ago

I was contemplating on choosing not enough info but then i said since only mary can win, mary is the only one sure to win. Eventually she would.

Dick He - 7 years, 2 months ago

Number of rolls needs to be clarified. If the game allows only finite rolls, Mary MAY, but not SURELY, win. If infinite rolls are allowed, Mary will surely win. This is a required piece of information to answer the question. As it is stated above, the answer ought to be "Not enough information"...

Dan McGinley - 7 years, 2 months ago

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yah...

Jonas Vega - 7 years, 2 months ago

even if finite rolls are there, probability of Mary winning is greater than zero. we have to find probability.

Manish Sagar - 7 years, 2 months ago

yes thank u

Pratik Zaware - 7 years, 2 months ago

great!unexpected explaination

Raksha Jham - 7 years, 2 months ago

figured it out... only when calculating --__--'

iliasse El mesnaoui - 7 years, 2 months ago

Its interesting ... if someone uses the complex ideas of probability and reply that there is no enough information.

Fazlu Bismi - 7 years, 2 months ago

Common sense, without doing any math, .0.000000001 probability will win against 0 probability

Manish Sagar - 7 years, 2 months ago

would u tell me what will be the ans if no of dices are 6

Akshay Gahlot - 7 years, 2 months ago

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With 6 dice, they could all land differently in 6! ways. They could all be the same in 6 ways.

Josh Silverman Staff - 7 years, 2 months ago

John will never win because dice only have 6 faces and he will win if all 7 dice have different faces, and it doesn't logic for John to win.

Solehuddin Wahid - 7 years, 2 months ago

But when I read the topic, I just thought that "the same" mean totally "same", i.e. 7 dice are the same :(

Thiên Thanh Ù - 7 years, 2 months ago

damnit

Patrick Chen - 7 years, 2 months ago

wow

Wonseok Song - 7 years, 2 months ago

I would like to clarify something. What does it mean to throw the dice differently?

Klahrinz William Catubig - 7 years, 2 months ago

classic

vaishnav garg - 7 years, 2 months ago

yes it's correct.i think in a foolish manner

Viswakanth Kandala - 7 years, 2 months ago

Misinterpreted the problem. I thought all of the dice have to me the same -.-

Leiko Ravelo - 7 years, 2 months ago

took me 10 seconds, 7 dice but a regular die only has 6 possible outcomes, that means throwing 7 dice will result to at least 2 outcomes among the 7 are the same.

Roi Vinson Abrazaldo - 7 years, 2 months ago

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in 7 dice, 1-1-1-1-1-1-1 or same logic will happen no matter how many tries it takes, but a different numbers will not happen for 7 dices because the most possible is 1-2-3-4-5-6-last one will either one among 1~6.

Roi Vinson Abrazaldo - 7 years, 2 months ago

Shiz. -_-

Joyce Almendrala - 7 years, 2 months ago

Hahaha :v thats right..i should have read more carefully

James Cho - 7 years, 1 month ago

i am a fool

san bha - 7 years ago

u r a genius

san bha - 7 years ago

oh, this one is a tricky problem. I didn't get it at first. I can't stop thinking who can win, with the many probabilities. I had learned one thing, use your common sense. hehe.

Hubert Hernandez Jr. - 6 years, 1 month ago

So true! Trick question!

Monette Pahlawan - 5 years, 5 months ago

We are only sure that John will never win. So right answer must be not enough information.

Xơ Rơ - 7 years, 2 months ago

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The question says that they will throw dice until someone wins , which means 1 of them has to win. Since it can't be John, it must be Mary.

Eric Aniag - 6 years, 6 months ago

Ahhh! I think I didn't get it, because it was written grammatically wrong! It should be: seven dices! not seven dice.

Pedram Shakerinava - 7 years, 2 months ago

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"seven dice" is correct. "dice" is plural already.

Eric Aniag - 6 years, 6 months ago

Ambiguous question. How does throwing the different dice differently differ from throwing them similarly?

(Correct/explain why Mary has more chances)

Kou$htav Chakrabarty - 7 years, 2 months ago
Jeremi Litarowicz
Mar 24, 2014

It is pretty obvious that you can't roll 7 different numbers between 1 and 6. Thus it is impossible for Jhon to win. Therefor Mary is bound to win eventually.

wrong question, it says "if ALL dice..."

Parker Prathyoom - 6 years, 1 month ago
Chandra Sahu
Mar 25, 2014

A dice has only six faces, so how can the seven dices will attain seven different scores??

They can't - and that's why Mary is sure to win eventually.

Pola Forest - 7 years, 2 months ago

Yeah I meant the same thing :)

Chandra Sahu - 7 years, 2 months ago

@Chandra Sahu That's the point of the question. This means that John cannot win, and Mary will eventually win. It may take a while though.

Matthew Stephenson - 7 years, 2 months ago
Samuel Wong
Mar 24, 2014

This is a tricky one. If there are 7 dices, they can't be all different.

So that means it's impossible for John to win, which means Mary is the one sure to win.

Pola Forest - 7 years, 2 months ago
Rindell Mabunga
Mar 24, 2014

John will never win because in order to win, John must roll all dice showing all different numbers but a regular die only has 6 sides. Therefore, the probability that Mary will win which is 7 / 279936 7/{279936} is higher than the probability that John will win which is 0 0 .

I think the probability should be 6/279936=1/46656 because Mary will win if and only if the dice show these 6 combinations, which are 1111111, 2222222, 3333333, 4444444, 5555555, 6666666. So, where is another combination?

敬全 钟 - 7 years, 2 months ago

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You have calculated the probability of Mary winning on her first roll. They are both going to play until on of them wins. Eventually this will be Mary because John cannot win.

Matthew Stephenson - 7 years, 2 months ago

but it does not necessarily imply that mary will win

SAYAK CHAKRABARTY - 7 years, 2 months ago

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That's why there is the word PROBABILITY

Mervin Bueno - 7 years, 2 months ago
Amresh Kumar
Mar 24, 2014

7 different landings are not possible. so, only mary will win.

Eddie The Head
Mar 25, 2014

There are 6 possibilities for each die and there are 7 dice..S all the dice cannot come up differently....So John can never win...So after some time Mary will win...

Harish Chauhan
Mar 25, 2014

because if we have 7 dice then it is definite to repeat one number atleast . So marry will win.

why doesn't any1 notice that even though chances of jon's winning are 0, still that doesn't mean that mary would surely win. her chance of winning is still 7/(6^7) because the question doesnot say that if one loses then the other is the winner!! the question could've been correct if it'd asked who would surely lose.

Somesh Singh - 7 years, 2 months ago

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Somesh Singh, I just say Marry will win. I didn't say what is the chances of winning her. Marry will win because it is definite that Jon will loose(because his winning chance is 0).

Harish Chauhan - 7 years, 2 months ago

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yeah i agree with u on that friend that jon's chance of winnin is 0, but the question doesn't say that if jon loses then mary surely wins; it could also simply be a tie!! until n unless the question specifies that they both try infinitely, it would be completely wrong to say that mary is sure to win!! please try to understand my doubt.

Somesh Singh - 7 years, 2 months ago

For the people that really need this - I changed the question, so now it says that they can throw it till infinity. I didn't think it was that hard though.

Pola Forest - 7 years, 2 months ago
Luca Ng
Jul 21, 2020

1/46656 chance 3_3

Christopher Unrau
Dec 20, 2015

There are seven dice. Therefore, not all of them can be different, and thus Mary wins.

Andrew Yang
Dec 19, 2015

This is a good example of the pigeon hole principle.

Let's say the first six people each rolled something different; the seventh person, whatever he or she rolls, will repeat one of the results that the other six got because a die only has SIX possible outcomes and there are SEVEN people.

So even though Mary's conditions are hard to meet, John's are IMPOSSIBLE.

Dhiraj Kumar
Nov 27, 2015

What was the name of the murderous math book of yours

Sabiha Sultana
May 3, 2015

a dice have only 6 sides so 7 different side is not possible but same 7 sides is possible.so mary is sure to win

Gracelin J
Jun 4, 2014

How can seven dices show differently if they have only six sides? So Its Impossible for John to win.

Rishabh Raj
Apr 12, 2014

awesome!

Finn Hulse
Apr 7, 2014

Impossible for John to throw the die differently seven times. :D

Sohit Miglani
Apr 2, 2014

simple,the dice have six different faces and seven dices cannot be fully different,atleast two shall carry the same no.

Amogh Jain
Mar 30, 2014

There are 7 dice and each has 6 faces so John can never win since at the least two dice will have same value.On the other hand Mary has probability of 1/46656 of getting the same value in all the dice. So Mary has the chances of winning.

Érico Bandeira
Mar 29, 2014

Com 7 dados... João não consegue ganhar porque sempre terá um dado igual

Krishna Garg
Mar 29, 2014

Since John gets different nos on dice,but each dice has six only,7th can not be different.With minimum different nos and 7th dice max 6 taken will make it total 27. While mary b can get gigher nos starting from 4,5 & 6. So Mary is sure to win

K.K.GARG,India

Ayan Bhuyan
Mar 29, 2014

Becoz there are six faces in a dice.. so seven different outcomes is not not possible

Pramod Parbhankar
Mar 29, 2014

As there are 7 dice and each dice has only six different faces it is impossible to get different faces at the same time i.e. at least two dice have same faces at the same time.(pigeonhole's principle)

Mahedi Prince
Mar 27, 2014

There are only 6 faces on a cube, so to have 7 different number is impossible. marry may be win but john has no probability .

Yash Karavat
Mar 27, 2014

A dice has six faces and hence at max six different outcomes. If there are seven dice, then it is sure that at least two dice will have the same number...

Kartik Umate
Mar 26, 2014

By using Pigeon Hole Principle it is clear that there can't be 7 different outcomes on a six sided dice........... so surely John can't win therefore Mary will win for sure

Arjun Suresh
Mar 26, 2014

Mary is the only person who can win the game. John can never win as throwing seven different digits with only six is impossible.

Kirity Mahanty
Mar 26, 2014

P(all seven dice have same number) = 6/6^7

P(all seven dice have diff number)= 0 because dice have only six faces and for seven dice at least 2 dice have same number on their faces. So all 7 with diff numbers is not possible.

Hence Mary is sure to win.

Swetanshu Prasad
Mar 25, 2014

no matter how many times the dice is thrown at least two dice will show the same good question.

You are expected to look for hidden facts before you start solving the puzzle. I was caught unaware too!

Jayashree Lakshmanan - 7 years, 2 months ago

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