Gone After Blackout

Logic Level 3

Each of four friends (Andy, Beth, Cici, Dave) ate 1 candy out of 11 leaving 7 in the bowl. A sudden blackout made the room completely dark, and when the light came back on, all of the 7 candies were eaten.

Andy first asked Beth, "Did you eat more than I did?"
Beth answered, "I don't know."

Then Beth asked Cici, "Did you eat more than I did?"
Cici answered, "I don't know."

Upon hearing these, Dave said he knew the exact distribution of the 11 candies.

If everyone is telling the truth, and is smart enough to catch the implications of the conversations, what is the distribution of the 11 candies that Dave figured out?

( 1 , 3 , 4 , 3 ) (1, 3, 4, 3) ( 2 , 2 , 2 , 5 ) (2, 2, 2, 5) ( 1 , 1 , 3 , 6 ) (1, 1, 3, 6) ( 1 , 2 , 3 , 5 ) (1, 2, 3, 5)

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6 solutions

Ben Wilson
Mar 16, 2014

When Andy asked Beth if she had eaten more than him, Beth replied that she didn't know. We can deduce from this that Beth had eaten at least 2 candies because if she had eaten only one her response would have been "No". When Beth asked if Cici had eaten more than her, Cici replied that she didn't know. Since we know that Beth had at least two candies (and Cici knows this as well), then we can deduce that Cici ate at least 3 candies, otherwise she would have said "No".

At this point Dave knows for a certainty the exact distribution of candies. The only way for Dave to know the exact distribution is for him to have taken the maximum number of candies while everyone else took the minimum, namely {1,2,3,5}. If Dave had only taken 4, then there would be some uncertainty (it could have been {1,3,3,4} or {2,2,3,4}) and he couldn't have honestly known the exact distribution.

first of all since she replied i don't know we cant rule out the possibility of yes or no .So logically the question doesn't have required information to deduce

Bharadwaj Medapuram - 7 years, 2 months ago

What shows that Andy has not eaten any?

Swapnil Dey - 7 years, 2 months ago

the question is more logical than algebraic. This type of question in my opinion should have been posted in a "logic" category or some sort.

Bonz Libiran - 7 years, 2 months ago

First of all that came to my mind , if anyone had eaten a maximum number of candy then the number will come up (so certainly i thought myself as dave's place)..and the question came up that how can i know the absolute distribution?? So i thought, i have had the maximum number of candy, 5 ...then the distribution can be equal for 3 of them...so i choosed (2,2,2,5) ...that was a really good question..and i guess i have to regret for it..

Orpz Bourn - 7 years, 2 months ago

I agree that Beth MAY have eaten two candies. But how sure are u that Cici knows that Beth had eaten two candies? There was no light after all. No one knows how much is eaten by each person.

Alfred Mark Aguilor - 7 years, 2 months ago

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Well, all four know that each of them has had at least 1 candy. Therefore, if Beth had only eaten 1 candy, then she would have replied with a certain "No, I have not had more candy than Andy", because there is no possible way for her to have eaten more than Andy's minimum of 1 candy if she has only had one. I must point out though, Dave is a greedy sod.

Jason Morley - 7 years, 1 month ago

She says she doesn't know if she ate more. She could have eaten two just as well as he could have eaten two. How does she know how many he ate. They were in the dark. The statement I don't know only means that beth at least ate one extra candy and cici also ate one extra candy or their answers would have been no. By the information given you have no idea how many pieces of candy the first person ate. Nor the total cici or beth at for that matter.

Billy Burgess - 5 years, 8 months ago
Lily Quartz
Mar 17, 2014

Andy=A Beth=B Cici=C Dave=D Lets ignore the first 4 candies eaten and add 1 to A, B, C and D at the end (for simplicity's sake) Clue 1. "Andy first asked Beth, "Did you eat more than I did?" Beth answered, "I don't know." "
Meaning B>=1 If Beth had eaten 0 then she would know for sure that she did not eat more than Andy (Andy cannot eat less than 0) Clue 2. "Then Beth asked Cici, "Did you eat more than I did?" Cici answered, "I don't know."" Meaning C>B: C>=2 Same logic as clue 1, Cici "is smart enough to catch the implications of the conversations" so she knows that Beth ate at least 1 candy. Therefore she ate at least 2 candies, if she ate less than 2 she would know for sure that she did not eat more than Beth. Clue 3. "Upon hearing these, Dave said he knew the exact distribution of the 11 candies." The only way for Dave to know the distribution for sure is if he had the maximum amount of candies possible and the others the minimum amount possible. If he ate 1 (or more) less than the maximum amount then he would not know for sure who that extra candy had gone to and would not know "the exact distribution". For Andy the minimum is 0, for Beth the minimum is 1, for Cici the minimum is 2, There are 4 left so Dave ate 4. Add 1 to each person (that we took off at the start) and you have A=1, B=2, C=3, D=5

Kunal Mandil
Mar 14, 2014

firstly beth answered that "he did't know", that means he must have eaten 2 or more than two candies because if he had eaten 1 candy he must have said no.

then when cici answered beth, he answered the same as beth did and even he has also listened that beth has told to andy that he don' know , that means he have eaten 3 or more than three candies as beth has eaten 2 or more candies then he must have eaten 3 or more candies

You can set some boundary conditions, Andy, Beth, and Cici could not have taken more than three candies. Because had any of them taken more than three they would have known that no one else could have had more candy and thus Andy would have no reason to ask Beth if she had more candy, nor would would Beth or Cici follow up, since they would know of their majority take on the candies

now dave knows about distribution that means he has eaten most candies and therefore the answer is 1,2,3,5

Really? You just decided to copy+paste someone's answer in the comment?

Wooil Jung - 7 years, 2 months ago

Plot twist: Dave had more rods in his eyes than normal and saw everything.

Bilal Akmal - 7 years, 2 months ago

i didn't found answer how 1,2,3,5 can any one explain in detail?

Pavan Kalyan - 7 years, 2 months ago

Can anyone explain the answer in detail ?

Pragya Nagpal - 7 years, 2 months ago

BETH DIDN'T KNOW BECAUSE THE LIGHTS WERE OFF AND SHE COULDN'T SEE (FAULTY QUESTION)

Andrew Rodriguez - 7 years, 2 months ago
Varun Agrawal
Mar 21, 2014

(A IS ANDY, B IS BETH, C IS CICI AND D IS DAVE) IF B HAD EATEN LESS THAN A, HE WOULD HAVE SAID NO (BOTH ATE AT LEAST 1. B MUST HAVE CONSIDERED THE POSSIBILITY THAT A ATE 1 ONLY WHILE ANSWERING, SO HE HAVING EATEN MORE AND NOT WANTING TO ADMIT, SAID HE WAS NOT SURE. BECAUSE THERE IS ALSO A POSSIBILITY CONSIDERED BY B THAT A ATE MORE THAN 1 JUST LIKE HIM AND MAY BE MORE THAN HIM.) SO B ATE MORE THAN A. SIMILARLY C ATE MORE THAN B. NOW D WILL SURELY IN HIS SOLUTION NOT INDICATE THAT HE ATE ANY CANDY WHEN THE LIGHTS WERE OUT. SO WE TAKE D=1. NOW C>B>A>1. NOW NEGLECTING (ONLY FOR NOW) THE FIRST ONE EATEN BY THEM, WE GET A+B+C=7. AND A<B<C. SO OUT OF ALL THE OPTIONS THE ONLY ONE SATISFYING THIS CONDITION IS A=5,B=3,C=2,D=1. HENCE THE ANSWER. .

Vaibhav Reddy
Mar 17, 2014

Don't know if this is an appropriate answer,please clarify that for me....

At first A A asked B B and B B said "I don't know"

So I thought "Okay, B B perhaps ate more than A A because he's like "I don't know.I didn't eat anything" "

I thought the same with C C too.... and then D D came out this way "Haha..I know the answer..."

If I assumed that A < B < C A<B<C and I will leave D D just out of the sum.

I came up with possibilities like * ( 1 , 2 , 3 , 5 ) (1,2,3,5) , ( 1 , 2 , 4 , 4 ) (1,2,4,4) * and many more.....

Sorry for giving such a pointless answer,just wanted to give out my views.....

The trick for me was realizing that they are all being honest. B said "I don't know" because she had at least one more candy. Otherwise she would have said "no". You can follow a similar reasoning to come to the inequality you mentioned in your post. The final clue is that Dave knew the exact distribution and the only way for him to know for certain would be for him to have taken 5.

Ben Wilson - 7 years, 2 months ago

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but why only 5 :/

Vaibhav Reddy - 7 years, 2 months ago

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Had Dave taken more, then it would have been impossible for Cici to have taken more than beth, and therefore would have answered "No", and had Dave taken less, there would have been an element of uncertainty remaining even after the two questions have been answered. The only situation in which Dave can answer with absolute certainty is the given result.

Jason Morley - 7 years, 1 month ago
Muhammad Refaat
Mar 9, 2014

Andy asked Beth if she ate more than him, so Andy probably didn't eat more during the blackout. Then Beth asked Cici, and both don't know who ate more, so both ate at least 1 more. Dave knew the distribution, so he is sure he ate more than anyone else.

Andy = 1+0, Dave = 1+4, Beth/Cici = 1+1 or 1+2 So, the solutions can be (1, 2, 3, 5) or (1, 3, 2, 5) and the one provided in the answers is (1,2,3,5)

I don't think several statements in your first paragraph can be deduced from the problem that way.

I'd agree that Beth ate at least one more (and hence doesn't know if she ate more than Andy).
We can then deduce that Cici ate at least two more (and hence doesn't know if she ate more than Beth).
Then, because Dave can deduce the distribution, it means that he must have eaten all the rest of the sweets.

Calvin Lin Staff - 7 years, 3 months ago

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You can set some boundary conditions, for instances, Andy, Beth, and Cici could not have taken more than three candies. Why? Because had any of them taken more than three they would have known that no one else could have had more candy and thus Andy would have no reason to ask Beth if she had more candy, nor would would Beth or Cici follow up, since they would know of their majority take on the candies. It should be noted that Dave now also has a boundary to how many he could have taken, since between Beth and Cici have taken at least 3 candies Dave can only take at max 4 candies. From this boundary condition and the implication that Beth took at least 1, Cici took at least two, and Dave needs a majority in order to deduce the distribution, which only happens when he takes 4 since that is the maximum amount of candies he can obtain, the answer cannot be {1,1,3,6} or {2,2,2,5} or {1,3,4,3}, plus it would also rule out a lot of other possible answers had this problem asked for a set of possible solutions rather than giving you the solutions. Just wanted to put that here in case someone wanted to try and figure out this problem without the use of the choices.

Nikhil Pandya - 7 years, 3 months ago

The statements are not more than you, so is it not possible that beth also didn't eat another candy making it equal to andy's candy count !!!

Sharad Rai - 7 years, 2 months ago

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No, Beth MUST have taken at least one candy. Why? When asked if she had eaten more Beth responded "I don't know" implying two things 1) She did not take a majority 2) She had to have taken at least 1 Why did she take at least one? Because if she did not take any then she would have responded "No" as there would be two cases to consider. First case: Andy ate more candy and she ate zero in which case her answer would be still true. Second case: They both had not taken anymore candy in which case the answer is still "No". This is because of the wording of the question. The statements "Ate more than" and "Ate the same amount or more than" are VERY different.Had they both taken the same amount (in this situation zero) neither had eaten more and thus the answer is "No".

Nikhil Pandya - 7 years, 2 months ago

But another way to see it is that Andy did ate more and only asked something to (hopefully) fool the others, so the answer 2,2,2,5 is also a logical one right, or maybe im just being too doubtful?

Khải Khù Khờ - 7 years, 2 months ago

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This does not satisfy the condition that Cici must have eaten at least two candies. Also it should be mentioned that none of them are lying, so he couldn't have been trying to fool them. Plus by setting boundary conditions and working backwards it can be shown that if Andy did eat a candy then it would be impossible to determine the distribution.

Nikhil Pandya - 7 years, 2 months ago

if andy didn't eat anything and beth asked asked her if she ate more than her, she would have said no! the fact that beth asked after the blackout means she ate during the blackout, answer should be 2,2,2,5. dave knew the answer because he ate 4 candies and only leave 3 candies which leaves the beth, cici, and andy wondering who ate more.

cyron masweng - 7 years, 2 months ago

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agree, Dave knew he ate max number of candies (from last 7) so there're only 3 candies left. he knew everyone ate at least one. Andy asked Beth that proves Andy ate at least one and wasn't sure if Beth took more than her. same case for Beth and Cici. So, the only logical answer is (2,2,2,5). but according to the given answer.... if Dave ate 3 (from last 7) he shouldn't know who (Cici) ate extra one.

Imran Ziad - 7 years, 2 months ago

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I agree with your post, that is exactly how I looked at it.

Rodolfo Mendoza - 7 years, 2 months ago

are u sure???....becoz if CICI didn't ask Davethat if he ate more than her then CICI knew that Dave didn't.......then he could not have eaten the most.....then the correct option should be (1,3,4,3)......as thats the only option where Dave didn't eat the most

Sayam Chakravarty - 7 years, 2 months ago

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Just because Cici didn't ask Dave does not necessarily mean that Cici has more than Dave. As well Dave must have a majority, since if he didn't then there could be multiple values for how many Andy took and he could not possibly know the distribution of the candies, Cici must have taken at least two, and Beth must have taken at least one. Secondly this problem requires backward reasoning, not forwards, starting with Dave and ending with Andy. Through this process we can eliminate {1,3,4,3} as well as other possible answers leaving {1,2,3,5} not only being the right choice, but the only choice in existence.

Nikhil Pandya - 7 years, 2 months ago

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how are u assuming that dave has a majority????....just becoz he didn't ask????.....then even i can assume that CICI didn't ask Dave becoz she knew that he didn't eat more...and reason backwards...???? we are here to solve problems not read minds or make assumtions like a fortune teller abt what the publisher of the question has in mind

Sayam Chakravarty - 7 years, 2 months ago

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@Sayam Chakravarty It isn't an assumption that Dave has a majority, more of a necessity, as it would be impossible for Dave to know the distribution if he did not have a majority, I already explained that. For this problem you don't need to read the mind of the publisher, you just need logic.

Nikhil Pandya - 7 years, 2 months ago

yeah.......several of the presumptions in the first paragraph are not necessarily possible or true

Rahul Vishal - 7 years, 3 months ago

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