Can't We Just Flip A Coin?

Albert and Bradley can't decide who will get the ball first in a game of basketball. Cathy decides to step in and tell them to pick an integer between 1 1 and 100 , 100, inclusive. Whoever is closer to the number Cathy randomly picked will get the ball first.

Albert randomly guesses the number 37. 37. Bradley then picks a number that will maximize his chances of winning. What number did Bradley pick?


The answer is 38.

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35 solutions

Agnes Fung
Feb 15, 2014

Albert picked 37. There are more numbers from 37-100 than 1-37; Bradly will have a larger chance of being closer to the number if he picks a number on the side of 37-100. However, if he randomly picks, he will be at an advantage because the distance from 37 to n could be equal to his number to n. He solves this problem by picking the next larger number, 38.

nice , really like ur answer///

ankur singh - 7 years, 3 months ago

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thank you :)

Agnes Fung - 7 years, 3 months ago

Me the boss.... Took answer 38 that is so correct

Jan Clevorn - 7 years, 3 months ago

(y) right agnes fung

Shalini Yadhav - 7 years, 3 months ago

wat if she says a number less than 37

Adhavan Manoharan - 7 years, 3 months ago

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Its about maximizing your chances. Choosing a number between 37-100 gives you a 63% winning chance where from 1-37 gives you only 37%.

Muhtashim Rafiq Chowdhury - 7 years, 3 months ago

why is it that everytime I answer in find your level it says answer must be in decimal?

cyron masweng - 7 years, 3 months ago

it can be less than 37 as cathy can choose no. less than 37 also Cathy had not only told to choose no. above 37. answer is wrong

Pranav Dev - 7 years, 3 months ago

wat abt 39

Pragyan Premarajan - 7 years, 3 months ago

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then if cathy chooses 38, it would be a draw....

Alan Ramos - 7 years, 3 months ago
Robert Fritz
Feb 14, 2014

My class at school was doing a debate in English and to see who would go first the teacher would pick a number between 1 and 10 and the closest person could say if they wanted to go first or second. So I thought, what would maximize my chances. For this problem it's 1 to 100, so it's still basically the same concept. Since Albert picked 37 the number that would maximize your chances of winning would be the number that gives you the highest chance, because there are more possible outcomes after 37 you would choose 38 so that the only way that you could lose is if Cathy picked a number that is 37 or lower which is a 37 percent chance of losing. On the other hand, if Albert choose 50, you could go either way because of the amount of outcomes of each side of 50 which is the same.

i really thinking of it .,but i answered 50.. goshh !

Rodney Ballatan - 7 years, 2 months ago

My answer is 38.......the reason depends on the chances.......as Albert picked 37, his chance to win is 37% by 100%.......to maximize the chance for winning Bradley should pick the number greater than 37....and....the nearest is 38.

Husnain Akbar - 7 years, 2 months ago

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if for number 37, chances are 37% as you say

i would pick 100 then for my chances to be 100%

then why did you choose 38 according to your statement.............!!

please reply positively...

why the answer wont be 50 !!!!

Rajat Pathak - 4 years, 12 months ago

49

Amado Naguib - 7 years, 3 months ago

38

Ruata Onmn - 7 years, 2 months ago

Why isn't it 50?

Pola Forest - 7 years, 2 months ago

hoho..got it..

Aiman Cool - 7 years, 2 months ago

I did it the same way... You simply have to use logic and think it through.

Ishan Maheshwari - 4 years, 6 months ago

ra

Ronwell Bolon - 7 years, 2 months ago

why it cant be 36?

dk chetan - 7 years, 2 months ago

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If it's 36, Bradley will only have a 36% chance of winning and Albert will have a 64% chance of winning.

Nathaniel Reyes - 7 years, 2 months ago

So nice of you.

Sadman Sakib Nishad - 7 years, 3 months ago

10

aravint aravint - 7 years, 3 months ago

i was gonna say 38 anyway

JiYoung Bang - 7 years, 3 months ago
Prasun Biswas
Feb 16, 2014

The number that would be chosen by the two players and the number Cathy has in her mind is between 0 0 to 100 100 (inclusive). Now, Albert guesses 37 37 . Now, we see that the range from 0 0 to 37 37 is smaller than the range 37 100 37-100 . So, the probability that the number in Cathy's mind is in 37 100 37-100 range is greater than the number being in 0 37 0-37 range.

Now, to maximize his winning, Bradley should pick a number in the maximum probable range (i.e., 37 100 37-100 range) and the number should be closer to Cathy's number and thus greater and closer to that of Albert. The closest number that can maximize his number after 37 37 which is both greater and closer to it will be 38. So, the answer is = 38 =\boxed{38}

thanx bro

Mayank Kulkarni - 7 years, 3 months ago

Yup..!!

GANESH RAJGURU - 7 years, 3 months ago

yes...!!

Jan Clevorn - 7 years, 3 months ago

nce answer

B Rajeswari - 7 years, 3 months ago

good analysis

Mamith Voola - 7 years, 3 months ago

yes it is!!!

Raffy Alabado - 7 years, 3 months ago

nice one

Thulasi Doss - 7 years, 3 months ago

Prasun Biswas's explation is the clearest one.

Sukanta Sahu - 3 years, 6 months ago
Himadri Shee
Feb 14, 2014

Since the number that Albert chose was 37, the number chosen by Bradley has to be 38. Then 63 numbers (38<=x<=100) would give him win.

SAurav TYagi
Feb 8, 2014

First thing is that the probability of Cathy choosing a number is same for any number from 1-100. But probability that the number she chooses is greater than 37 is more than that of the number being less than 37. Therefore to maximize his chances of winning, Bradley should choose a number greater than 37. Also the number he chooses should be closer to the number Cathy chooses therefore the number he chooses should be 38.

At noon you have 2 smarties in a bowl.Every minute they double their number (2, 4, 8, 16.....) By 2 pm the bowl was full. At what time was the bowl half full?

yaashi pathak - 7 years, 3 months ago

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ohh god.. soo many smarties.. what will someone do with them... anyways.. right ans is 1:59 ... it was tooo easy.. actually a did something idiotic ... i calculated all number of smarties when the bowl was full.. but its not important .. there's a logic that. at every minute they become double.. soo if bowl is full at 2 pm .. soo it must be half at just a minute before 2 pm.. :D :D

Rishabh Tripathi - 7 years, 3 months ago

Thats a lot of smarties!

Harjit Natt - 7 years, 3 months ago

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Since we are doubling the amount of smarties each time it would just be 1 minute less than the final time, in this case 119 minutes from 12 or 1:59pm

Harjit Natt - 7 years, 3 months ago

The biggest bowl ever!! You will never see that big bowl in your life neither you can imagine it!! XD XD XD

yaashi pathak - 7 years, 3 months ago

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@Yaashi Pathak The full bowl is about 7.2 times more massive than η Carinae, one of the most massive stars known.

A Former Brilliant Member - 7 years, 3 months ago

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@A Former Brilliant Member How did you find that O_O

Tan Li Xuan - 7 years, 3 months ago

1:59 pm :)

Tan Li Xuan - 7 years, 3 months ago

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Perfect!! :)

yaashi pathak - 7 years, 3 months ago

1:59 p.m

Shalini Yadhav - 7 years, 3 months ago

1:59

Faiz Akhtar - 7 years, 3 months ago

1:59

Shreesh Naidu - 7 years, 3 months ago

Cool..!!

GANESH RAJGURU - 7 years, 3 months ago

nice

Ashfaq Khalil - 7 years, 3 months ago
Thadeu De Paula
Feb 16, 2014

There are more numbers between 37 and 100 than between 1 and 37. So there are more chances in the range of between 37 and 100. Choosing 38 all the numbers after it will benefit this choice. So, more numbers will near 38 than 37.

This was the easiest answer for me to understand.

Rose Huntress-Ristich - 7 years, 3 months ago

In the event the first person had chosen 50, wont the second person have to guess at random?

Diyah Muhammed - 4 years, 2 months ago
Everson Dantas
Feb 16, 2014

We only have to think a little... the numbers need to be between 1 and 100, inclusive, and Albert picked 37, so obviously if Bradley choose 38 he has more chance to win, cause he wins with any number between 38 and 100, inclusive, which gives more options than 1 to 37. No calculation need.

Eric Downes
Mar 12, 2017

If the numbers chosen by Cathy were uniformly distributed, the answer is 38, as the other answers detail, because there are more integers to choose in the interval [38,100] than [1,36].

However, people are pretty bad random number generators! I think that the uniform distribution is a poor prior. It is an empirical question which of those intervals above would actually get picked more often by real people . Since we are more intimately familiar with numbers on [1,10] than numbers closer to 100, there's a good chance that the interval [1,36] could actually contain more statistical weight!

Do the experiment "choose a random number on [1,100]" with your friends and report back!

Hadia Qadir
Jul 28, 2015

First thing is that the probability of Cathy choosing a number is same for any number from 1-100. But probability that the number she chooses is greater than 37 is more than that of the number being less than 37. Therefore to maximize his chances of winning, Bradley should choose a number greater than 37. Also the number he chooses should be closer to the number Cathy chooses therefore the number he chooses should be 38

Maths Perera
Apr 8, 2014

It is 38 as the only way the Bradley could lose is if Cathy chose a number less than 37 and the chances were that this was unlikely. Thus, Bradley's choice helped maximise the chance of getting it right.

Ajay Reddy
Mar 26, 2014

Think of a number line with 1 to 100. Albert is on 37. If albert is on 38 leaving numbers before 37, he can win for all 63 numbers.Any other place will have less numbers that he can win for.

Dinesh Inspire
Mar 21, 2014

1-37 range is smaller than 37-100 range. Bradly will have a larger chance of being closer to the number if he picks a number on the side of 37-100. However, if he randomly picks, he will be at an advantage because the distance from 37 to n could be equal to his number to n. He solves this problem by picking the next larger number, 38

Julieta Ramos
Mar 20, 2014

38-100 has a larger chance of guessing the answer correctly than 1-37..

Saurav Sharma
Mar 19, 2014

keep it simple.............

Rudra Arora
Mar 9, 2014

38(Albert picked 37. There are more numbers from 37-100 than 1-37; Bradely will have a larger chance of being closer to the number if he picks a number on the side of 37-100. However, if he randomly picks, he will be at an advantage because the distance from 37 to n could be equal to his number to n. He solves this problem by picking the next larger number, 38.)

Diptesh Pipaliya
Mar 8, 2014

bcz of the catchy says whoever chose max no his will get the basketball in the goal..

0000

aravint aravint - 7 years, 3 months ago
Subir Das
Mar 7, 2014

the number may be less than, equal or greater than 37. The possibility is greater that it is above 37 for there are as many as 63 such numbers till 100. So the number Bradley should pick is 38 so that any number greater than 37 will be closer to it.

38

Jovanny Tumilap
Mar 6, 2014

yeah! i did solve it ^_^

Usman Ashraf
Mar 2, 2014

We only have to think a little... the numbers need to be between 1 and 100, inclusive, and Albert picked 37, so obviously if Bradley choose 38 he has more chance to win, cause he wins with any number between 38 and 100, inclusive, which gives more options than 1 to 37. No calculation need.

37 is placed to the bracket 1-37 by the second guesser who gave number 38 which is from the bracket 38-100. Therefore, the bracket 38-100 (with 63 numbers) have more chance than the bracket 1-37 (with 37 numbers).

Bharat Raj
Mar 1, 2014

as the previous ones is 37, the next possibility for wiining the ball.. n0. must be between 38 to 100, if we choose the next no. of 37, then any no. after 38 will be the answer

Sơn Trần
Mar 1, 2014

Albert picked 37. There are more numbers from 37-100 than 1-37; Bradly will have more chance of being closer to the number if he picks a number on the side of 37-100. So he should chooses number 38

Ganesh Alat
Feb 28, 2014

if cathy chooses the number 37 0r below 37 there are 37% chances of loosing ,by choosing 38 there are 63% chances of winning

Suresh Dvv
Feb 28, 2014

if cathy chooses number less than 37 including 37 then definitely albert will be d winner and now as the second one who has to maximize his chances of winning the second one has to choose 38 as if cathy chooses number beyond 37 he will be the ultimate winner as he will be the nearer to it and now his chances of winning is 63% while for albert is 37%

Nikitha K
Feb 26, 2014

Since Albert randomly guessed 37, you would have to see if there are more numbers from 1- 37 or 37- 100. Once you realize that you have to choose 38 the next number after 37 to make sure you will be closer to the answer than Albert.

Aniruddha Singh
Feb 24, 2014

38 .We assume that the event of the girl choosing any no is equally likely of her choosing any other . In that case each no has probability 1/100.Since 37 has been chosen .The total probability that the girl chose a no >37 =63/100 which is higher than the probability of her choosing a no<=37(37/100).So the guy will choose a no in the former region.Now to ensure that he wins if any no >37 is thought of he has to choose 38 because then it will be sure that if she chooses any no >37 he will be closer to it than the other guy.

Yogesh Ghadge
Feb 24, 2014

1-37 have less numbers than 38-100 so the chances of getting write answer is greater

Akshay R-ya
Feb 19, 2014

it is given that bradley has maximum chances. it means that the number picked by bradley is greater than Albert.and albert has choosen 37. and 38 is just greater than 37 which creates more chances of winning.

Praneeth Madhira
Feb 19, 2014

Since 37 was picked by Albert, Bradley picks 38. This is because there is a greater chance of Cathy selecting a number greater than 37 than a number less than it. Thus 38 would be one number closer than 37, to any number which comes in that range.

Aditya Deodhar
Feb 18, 2014

Since Albert chose 37, and Cathy picks a number randomly, the probability that her chosen number lies between 1-36 is 36%, and the probability that it lies between 38-100 is 73%. So Bradley must choose a number greater than 37 to maximize his chances. Now if he chooses a number x, such that 37<x<=100, then the probablity that his chosen number is closer to Cathy's is (100-(37+(x-37)/2). This is maximized when x=38.

Kaniska Kumar
Feb 16, 2014

i thought generally in a simple way that if albert picked a number is 37 then i thout a number should be > than from albert's number,so i picked up a number 38 & fortunately its correct.woww...amazing

Dick He
Feb 15, 2014

The answer logically must be 38. If Bradley were to chose 38 then if Cathy's number was from 38-100 he would win. If he chose a number below 37 then 37 would win if the number was between 37-100 which the at most 36 possibilities would be less than 38-100. If it were 39 then 38 would be a tie which then there would be a tiebreaker. This lowers it by one possibility and going higher only makes it worse. If Bradley wants to obtain the best chance of winning he must have chosen 38.

Varun Suvarna
Feb 15, 2014

It's very simple. To determine the number chosen by Bradley, we have to judge 2 things, (i)From which half the number should be chosen &(ii)At what distance from 37. Albert has chosen 37 which is less than 50, so in-order to increase his chances he will choose from the right half. Also to minimize the chances of loosing, he will choose a number next to 37. Thus, keeping both things in mind, Bradley will choose the number '38'. (Note:-->the term 'half' is used to depict the left{less than 37} & right{more than 37} side of the list 1-100 taking 37 as the central number)

Callum Farnden
Feb 15, 2014

Bradley should guess one of the integers that would be adjacent to the number Albert picked - as he picked 37, this would suggest either 36 or 38. There are more numbers where 38<B<100 than where 0<B<36, thus he should pick 38.

i like this

Raja MRaja - 7 years, 3 months ago

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