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# Biology

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Actually - when a cell divides each cell starts out 1/2 as big. So even though the number doubles every minute - the same CAN'T be said about the size. So if the plate was full at 12:00, it was pretty much full at 11:59. Growth and division are not the same thing.

try reading the puzzle first without changing it to fit your own stupidity. This wasn't even a logic problem. They give you the answer right in the question. Anyone who didn't get this one has got some serious IQ issues.

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depends on when the organisms started dividing or when they were put in the bowl

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11:59 it doubles every minute

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• 1 month later...

a cell is half as big as it was when it divides, but there's two of them, so the time stays the same. However, it increases in size, so it would be half full at 11:59, but also shortly before. However, there is no way of telling that it takes exactly a minute to reproduce, so there is no definite answer

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• 4 weeks later...

I really like this brain teaser because it isn't as easy as it seems and looks. I agree with the last person's post; aside from all of the complications resulting from nutrition of these organisms, the dish was half-full at 11:59:00 and less than a minute prior to that. So, that also means that the dish was full at 12:00:00 and less than a minute before that time. Since the cell has to double in size before dividing (according to mitosis), in a perfect world there are two times when the dish is full and empty - just before the organism splits and just after division.

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11:59. If it doubles itself eeach minute, then at 11:59 it is half the size it will be at 12:00.

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• 1 month later...

this is so easy.and im a 5th grader

11:59 to easy

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Yeah, seriously - just read the riddle and take it at face value. I am a molecular biologist and I'm not going to get all anal on wording. I mean, how many cells actually go through a full cell cycle in one minute?? It's like going to the movies and watching a movie like "Braveheart" for historical accuracy. IT'S AN AWESOME MOVIE, but I don't really think everything in that movie was right. On top of it, had the movie had been made completely accurate, would it have been as good? Probably not - same on the riddle. If you start adding 3 million caveats, it gets confusing and not as fun to read. Purpose of these are for FUN, not to TRY to look smart by pointing out esoteric facts that are obviously not meant to be incorporated into the puzzle.

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11:59. -1 minute = -1/2 of the cells.

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But guys, it's a logic puzzle, not an AP Bio question. Itâ€™s asking you to look at a problem as a system of variables- â€˜real worldâ€™ issues arenâ€™t meant to apply, because that would take the logical reasoning out of the problem. Running to your text book to find out the growth rate of the common cell/ organism and itâ€™s food consumption defeats the purpose of basic reasoning skills.

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it depends on how you interpret the question. If when the original cell divides into two of equal size- if that means the volume of the two cells ( the sum of both cells) equals the size of the one original cell, and 4cells of equal size also equals the volume of the original cell, then the answer is, it was full from the beginning- full of one big cell that kept dividing into smaller cells of the same volume.??

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yep 11:59 although i would like to point out that even the most primative organism will never divide that fast now change that to E.coli and every 20 minutes then it would be entirely possible

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• 3 weeks later...

It would have to be 11:59

11:59 Duh

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the question isn't worded very well. it still says "Let's say some primitive organisms divide themselves every minute in two equal parts which also divide the next minute and so on." 2 equal parts doesn't mean the same size as original organism.

a better wording would be "Let's say some primitive organisms divide themselves every minute in two equal parts that are the same size as the original organism, and which also divide the next minute and so on."

I disagree, cells go through division only after they have grown to their full size, they would split, then grow again, and so on, so as such stating that they are the same size as the origional isn't necessary.

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Actually - when a cell divides each cell starts out 1/2 as big. So even though the number doubles every minute - the same CAN'T be said about the size. So if the plate was full at 12:00, it was pretty much full at 11:59. Growth and division are not the same thing.

Actually, when a cell divides it starts out the same size as every other cell. The 2 cells that form are the same size as all the other cells in the body also. I think the person who wrote this comment got confused because reproductive cells have a hypoid (1/2) number of chromosomes until they met with another, then they become diploid(1). The number of chromosome does not make a difference. Also, technically, they didn't say anything about it growing. It said that the cell divides, when this happens, the cells copies itself. It is called dividing not because its gets smaller, but because it copies while it breaks apart. Cells dividing are the same as cells multiplying. That is how we grow. Because cells divide, so it is the same thing when it comes to cells. I am taking a biology class right now although they teach these things in 7th grade.

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• 4 weeks later...

11.59 am

Edited by andyrew92
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its realy simple actually. some people are caught up with trying to reason it out but since its a riddle u need not just a willing suspension of disbelief but also to put aside any scientific facts. in other words it doesnt matter the rate at which cells grow die or eat. this might be called biology but it is a simple math riddle. it states that the new borns here are same size. so every minute u have 1 more for every organism before at the same size hence taking up exactly twice the space. reverse the process its half the space every minute prior to any particular minute.

the starting time doesnt matter since that varies in according to the actual size of the bacteria and the pan. none of these are needed to know when it was half full since when it was full is given. thus the answer is like so many people have said: 11:59 A.M. Its not at all a complicated riddle but one of the easiest on this page. Just remember not to over think it with scientific facts and the such.

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• 2 months later...

You don't have to know what time it started. You know what time it was full (not checked and found to be full), and you know how long it takes to double the quantity of the orgs. Taking into account that new orgs are the same size as the original, the orgs. double their quantity in 1 minute, and that the end time was 12:00, the dish had to have been half as full a minute before.

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• 2 weeks later...

11

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• 8 months later...

So, I am going to take a stab at this, and there is no guarantee that this is right because it has been a few years but here it goes:

.5/43=x/60

to solve for X the equation read: (I used the * as a multiplication symbol so as not to be confusing)

60/60 * .5/43 = x/60 * 60/60

30/2580 = X

3/258 = X

3/258 = .01 per minute

.04 *43 min = .43 (which is half)

.43 * 2 = .86 to be full

So, it would take 86 minutes from start to finish to be full

So, 12:00 + 86 minutes = 1:26

So, at 1:26 the dish should be full.

Any chance that is close to right?

Edited by cari2483
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Wait...I just thought about it and realized I did all that work for nothing LOL. If the dish was half way full at 12:43 and every minute, the organisms double, then at 12:44 the dish should be full...right?

Like I said in the previous post, it has been a while and the scientific size of the organism aside I still didn't see how 11:59 could have been the right answer, even after reading all of the posts.

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Wait...I just thought about it and realized I did all that work for nothing LOL. If the dish was half way full at 12:43 and every minute, the organisms double, then at 12:44 the dish should be full...right?

Like I said in the previous post, it has been a while and the scientific size of the organism aside I still didn't see how 11:59 could have been the right answer, even after reading all of the posts.

well spotted

answer for old wording is 11:59

answer for new wording is 12:44

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• 5 months later...

I believe the point of the exercise has been missed: Its a logic puzzle, not a Biology question. The answer is 12:44 (in one more minute) because 1/2(amount of petri dish full) x 2 (the number of cells after each divide) = 1

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• 2 weeks later...

12.44

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This topic is now closed to further replies.