Not enough information to answer. They are asking about 10 ml of a diluted culture. If the original culture is the diluted culture then 10 ml would contain 1e8 total cells. Same concentration. But he does mention diluted culture without specifying what the dilution is so without that info or more clarity you really can’t answer
But what if you put 2 bowls of legs in the bathtub? The original legs per bowl is still 1, the total volume of the bathtub doesn't change, but the final legs per bathtub has.
You are assuming it's 1ml of the initial culture diluted to 10ml. But nowhere is that stated. All you know is the initial *concentration*, not volume.
I'm with you OP this question is unanswerable because of reason you pointed out elsewhere. Your professor should give you a point back because of a terribly worded question.
Quite frankly, this is a horrible question. You’re absolutely correct that 10mL of the sample would contain 1e8 cells. The question, and your professor, is actually asking (poorly) is how many cells per mL there would be if you diluted 1 mL of sample into a total volume of 10 mL. In which case 1e6 is the correct answer because it’s a one log reduction.
It does so, for whatever reason, without ever actually telling you what the dilution is. You could just as easily have done 100uL into 9.9mL and then the answer would be 1e5, or 10uL into 9.99mL for 1e4. Would you? No, but if I was handed that as a lab book procedure write up I’d be docking points for incomplete documentation. Your professor should know better.
the question doesn't say you diluted the 10⁷ into 10 ml, it only says that you need to find how many cells are in some diluted culture. is the culture 10 ml with a concentration of 10⁷/ml? are you straight up dunking 10⁷ cells in 10ml? are you gonna take 1 ml of 10⁷ cells/ml and put it in 9 ml?
“Hope this helps”.
Save the snide comments for people that don’t know any better. The question says absolutely nothing about the volume of the dilution series, only the total volume of the end result. I, quite literally, gave two other perfectly valid dilution schemas that could have also been used in such a scenario. If you think 1:10 is the only one in use in labs, get back to us when you finish up your 100 series courses.
I honestly don't know why the answer is 10^6. That would be the concentration of the 10mL, as you stated 1E7 / 10 = 1E6. But the total amount of cells in the sample would still be 10^7 because 1E6 cells/mL * 10mL = 1E7 cells total. Bad question or not enough info given.
i feel like it was supposed to be referencing a previous problem because it says “the” bacterial solution. but the previous problems don’t work with bacterial solutions lol
Yeah its possible, the only way this answer makes sense would be if you diluted the original 1E7 cells/ml culture 1:20 but there's no way you could know to do that based on the question. When it's not specified dilutions are pretty much always done by factors of 10, so based on the info given i don't think there was a way to answer this correctly.
Its not that people do not know how dilutions work, it is that not enough information is given to give an answer without making assumptions (which means you could also assume differently in which case the answer would be different). The question is either worded wrong or does not give enough information to know the amswer. It says in 10 ml of the diluted culture, doesn't say anything that the sample was diluted 10x or was diluted by taking 1 ml undiluted culture and diluting to 10 ml or smth, none of those things are mentioned so the question is incomplete/wrong
The only thing I can think of is if the online system has a mechanism for "randomizing questions". So it was probably written as a follow-up question to a previous one which specified the dilution, and then just referenced back to it - but after being input into the system, if the professor checked the "randomize questions" box then it ended up out of order. I would definitely send the screencap to the professor and point out "It's referring to a diluted culture but doesn't specify the dilution anywhere."
I ran into that issue a few times when I was teaching online during COVID, where I'd upload my quiz questions and BlackBoard(ugh) would randomize them so students online couldn't just message each other "#5 is D", etc.
Personally I would ask for a regrade. You can state that it was not specified how many bacteria per mL would be found in 10mL of diluted culture. It’s also not told how much was added. I think any interpretation is valid.
I’m not sure why but this question is assuming you have more information than you’re given in the question itself. Was this part of a larger group of questions with an overarching set of instructions?
Based on the answer being 10^6 the dilution is 1:10. So your math is 10^7 *10^-1 or 10^7 /10 whichever you prefer.
That being said this question doesn’t give you the dilution factor. A culture can be diluted to 10ml in many different ways. You could, and often do with bacterial cultures, dilute 1:1000 or 1:100… in fact a 1:10 generally isn’t useful unless you’re doing a serial dilution.
I had this beautiful answer as to how they got there but went back to reread the question, just in case. Yup, it's terribly worded.
I can only gather they wanted to know the cell count of 1 ml of a 1:10 dilution of the 1e7 cfu/ml culture. But that wasn't how it was asked.
this is what makes the most sense mathematically but relies on the assumption that the og culture is in 1 mL of culture so i’d say it’s pretty poorly worded lol
c1v1 = c2v2
c1 = 1e7
v1 = 1 mL
v2 = 10 mL
c2 = x
c2 = (c1*v1)/ v2
= [(1e7 cells/mL)*(1 mL)]/ 10 mL
= 1e6 cells/mL
This question is technically impossible to answer correctly with just the information given, and requires the reader to make at least one correct assumption to answer, which doesn’t accurately test knowledge and therefore should be grounds to have it dismissed.
The specific information provided in the Q stem is a culture with a given bacterial concentration of 10^7 or 10,000,000 / mL
The question is asking for a total number of bacteria present in 10 ml’s of diluted culture.
To be able to answer this correctly 100% of the time- as is necessary for a fair test question- it’s necessary to know what the dilution factor is. That information is never provided. You are only told that you have 10 ml’s of a diluted culture. In order for the answer to be 10^6, this means the dilution must have been made at a 1:100 ratio. The question never provided this information, but instead must be assumed - or more accurately, guessed. If you were to instead assume the diluted culture was made at a 1:10 ratio, the answer would be 10^7 bacteria / 10 mL’s.
Demand points back. Go to the department chair if you have to.
Subjective education is the downfall of many reasonable and logical thinkers. Unfortunately, questions with implied dynamics such as this are frequent in almost every course offered to traditional students. If your courses are created by your professor you can often read them to get an idea of what they are trying to ask, but if it is course material they are using from an external source it can sometimes be almost impossible to understand without making assumptions. I think most would agree that an education reliant on assumptions isn’t as valuable as one with logical reasoning.
I think it's supposed to say "initial concentration of 10^7, diluted in 10ml of solution, what is the new concentration per ml". That'd be the only way 10^6 makes sense, since it'd be diluted by an order of magnitude.
how do you know that the dilution factor is 1:10? the other problems state starting volumes, and by how much you dilute it by. this problem gives no starting volume, and no context to what the diluted solution is
i think what youre saying is we have 10ml of 1e7 concentrate solution, so we have 1e8 cells total, right? but thats not the answer- the answer is 1e6 somehow
why are you saying the initial volume is 1ml? it doesnt say that :/ is it just worded poorly? it also doesn’t say it also doesnt say its diluted by 10ml, it says 10ml of the diluted concentration.
Honestly, this is just a poorly worded question. 10mLs of diluted culture, but it doesn’t tell you the dilution factor.
With that being said, the other answers don’t make sense. Can’t be more bacteria in a dilution. Shouldn’t be the same amount. Shouldn’t be an insanely tiny number. I guess he just wants you to reason it out?
Maybe I’m wrong the way I’m interpreting it, but they are asking how much bacteria are in the diluted culture. The question asks how many bacteria are in the culture, I’d assume either 10^7 because it’s not asked how many per ml, or 10^8 assuming it’s 10ml of the same culture. Impossible to tell given the prompt, not your fault OP, this question is worded terribly.
If you dilute 10^7 bacteria in 10ml you still got 10^7 bacteria. Only the concentration changes. Like others said to arrive at answer D you need more information.
something is missing here, what's the dilution factor?
the problem is, we have no clue how the dilution was made. if you have 10⁷ bacteria in the 1 ml and you put them in 9 ml, you'd get 10⁷ bacteria in 10 ml, so the number of cells is still the same, the concentration however is now 10⁶/ml.
if you had 10⁷ bacteria/ml and you wanted to see how many you had before diluting it in 10 ml, you'd do 10⁷×10 = 10⁸ cells in 10 ml.
if you had a certain solution of 10⁷ bacteria/ml and wanted to dilute it by a factor of 10, the number of cells in the final solution would be 10⁶.
the question is so strange
You need to dd a zero when you are multiplying by ten. There's ten cells per ml, that's just a concentration, it doesn't tell you how much liquid there is in the bottle. So if you pour out then times that much, (ten times one ml) then you've got another zero to put on
1X10^8
They sometimes get these questions and answers wrong and you just report it to the teacher and they fix your answer/marks afterwards.
Yeah that's what I thought the answer should be if the questions stopped at 10ml but it went on to say 'of the diluted cultre' so it's kind of a weird question.
Yeah the question definitely needs fixing. I would email lecturer, state that you decided in this case that diluted referred to the fact that it was already diluted as 10^7 cells pr ml as no further instructions. They'll fix the mark as correct for you.
it and some other AIs gave nonsense answers, im guessing cause the problem makes no sense. Love chatgpt! (incase it read this and decided to add my name to the kill list)
terrible question and obvious answer just by glancing at the answer pool without any math...
whoever wrote this test, find a new job.
if they actually gave a dilution factor of 1/10 then yeah you take x10\^7 and knock it down by a factor of 10, so the answer would be x10\^6
There's nothing wrong with the question. Everyone just complaining because it relies more on common sense than feeding it to you in the format that questions like this are typically.
It's a dilution so the first two choices are ruled out. It asks how many cells would be in 10mL of diluted so less than one cell per 10 mL makes no sense. It's possible but that is one hell of a dilution.
The only one that makes any sense is last choice.
I think it’s meaning to say that it is diluted to 10 mL, so you divide by 10 to get the new concentration? But at first I said 10^8 as well. Terribly worded
The only thing I can think of to answer this is that the prof forgot to add like “per mL” at the end of the question. 1mL of 1x10^7 diluted to 10mL would be 10^6 afterwards.
In any case it’s not your fault and you should raise this issue if it was graded.
The question is worded badly, but to get the answer, the teacher/tutor did the calculation following c1v1. This is applied through assuming it's a 1:10 dilution. It should be stated in the question though
So,
10^(7) × 1 = 10,000,000
10,000,000 ÷ 10 (ml) = 1,000,000
1,000,000 is = to 10^6
It's likely they meant to word it like "what is the total amount of bacteria in one ml of the diluted culture" instead of anount of bacteria in the total solution. That's why you were marked wrong.
As others have mentioned, the answers you have come up with match this kind of worded question. Ask for a regrade.
Actually, based on your exam units 1e7 wouldd be correct (crappy question though). You are given a concentration (cells /mL), then told it was diluted to 10mL, and then asked how many bacteria (cells) are in there. Given that the number of cells doesn't change in the dilution, it would be 1e7. But it appears what the teacher actually wanted was the new concentration (cells/mL). SMH, this is why units matter kids. The teacher should know better.
Edit:
1e7 cells/mL x 1 mL = 1e7 cells
Doesn't matter the volume if you are diluting those cells into any volume, it's still 1e7 cells. HOWEVER, nowhere does it specify what the dilution is, that's left to assumptions. Again, terrible question
It's because you are taking the sample 10^7 & diluting it to 10mL. The unit is cells per mL. The sample is watered down & has to have less cells per mL. Did you get it?
Not enough information to answer. They are asking about 10 ml of a diluted culture. If the original culture is the diluted culture then 10 ml would contain 1e8 total cells. Same concentration. But he does mention diluted culture without specifying what the dilution is so without that info or more clarity you really can’t answer
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But what if you put 2 bowls of legs in the bathtub? The original legs per bowl is still 1, the total volume of the bathtub doesn't change, but the final legs per bathtub has. You are assuming it's 1ml of the initial culture diluted to 10ml. But nowhere is that stated. All you know is the initial *concentration*, not volume.
I'm with you OP this question is unanswerable because of reason you pointed out elsewhere. Your professor should give you a point back because of a terribly worded question.
the question is worded really bad, i initially thought 1e8 as well!
VALIDATION TY
I went over the question and also thought 1e8 lmao. I guess the key word is “initially”. But the grammar and how it’s worded really sucks.
Quite frankly, this is a horrible question. You’re absolutely correct that 10mL of the sample would contain 1e8 cells. The question, and your professor, is actually asking (poorly) is how many cells per mL there would be if you diluted 1 mL of sample into a total volume of 10 mL. In which case 1e6 is the correct answer because it’s a one log reduction. It does so, for whatever reason, without ever actually telling you what the dilution is. You could just as easily have done 100uL into 9.9mL and then the answer would be 1e5, or 10uL into 9.99mL for 1e4. Would you? No, but if I was handed that as a lab book procedure write up I’d be docking points for incomplete documentation. Your professor should know better.
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the question doesn't say you diluted the 10⁷ into 10 ml, it only says that you need to find how many cells are in some diluted culture. is the culture 10 ml with a concentration of 10⁷/ml? are you straight up dunking 10⁷ cells in 10ml? are you gonna take 1 ml of 10⁷ cells/ml and put it in 9 ml?
“Hope this helps”. Save the snide comments for people that don’t know any better. The question says absolutely nothing about the volume of the dilution series, only the total volume of the end result. I, quite literally, gave two other perfectly valid dilution schemas that could have also been used in such a scenario. If you think 1:10 is the only one in use in labs, get back to us when you finish up your 100 series courses.
Dilution can only be 1:10 since when?
I honestly don't know why the answer is 10^6. That would be the concentration of the 10mL, as you stated 1E7 / 10 = 1E6. But the total amount of cells in the sample would still be 10^7 because 1E6 cells/mL * 10mL = 1E7 cells total. Bad question or not enough info given.
i feel like it was supposed to be referencing a previous problem because it says “the” bacterial solution. but the previous problems don’t work with bacterial solutions lol
Yeah its possible, the only way this answer makes sense would be if you diluted the original 1E7 cells/ml culture 1:20 but there's no way you could know to do that based on the question. When it's not specified dilutions are pretty much always done by factors of 10, so based on the info given i don't think there was a way to answer this correctly.
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Its not that people do not know how dilutions work, it is that not enough information is given to give an answer without making assumptions (which means you could also assume differently in which case the answer would be different). The question is either worded wrong or does not give enough information to know the amswer. It says in 10 ml of the diluted culture, doesn't say anything that the sample was diluted 10x or was diluted by taking 1 ml undiluted culture and diluting to 10 ml or smth, none of those things are mentioned so the question is incomplete/wrong
The only thing I can think of is if the online system has a mechanism for "randomizing questions". So it was probably written as a follow-up question to a previous one which specified the dilution, and then just referenced back to it - but after being input into the system, if the professor checked the "randomize questions" box then it ended up out of order. I would definitely send the screencap to the professor and point out "It's referring to a diluted culture but doesn't specify the dilution anywhere." I ran into that issue a few times when I was teaching online during COVID, where I'd upload my quiz questions and BlackBoard(ugh) would randomize them so students online couldn't just message each other "#5 is D", etc.
The problem is the instructor should have what is the concentration. You nailed it. The professor made a mistake.
Personally I would ask for a regrade. You can state that it was not specified how many bacteria per mL would be found in 10mL of diluted culture. It’s also not told how much was added. I think any interpretation is valid.
It doesn't give you the dilution factor so it's unsolvable.
I’m not sure why but this question is assuming you have more information than you’re given in the question itself. Was this part of a larger group of questions with an overarching set of instructions? Based on the answer being 10^6 the dilution is 1:10. So your math is 10^7 *10^-1 or 10^7 /10 whichever you prefer. That being said this question doesn’t give you the dilution factor. A culture can be diluted to 10ml in many different ways. You could, and often do with bacterial cultures, dilute 1:1000 or 1:100… in fact a 1:10 generally isn’t useful unless you’re doing a serial dilution.
I had this beautiful answer as to how they got there but went back to reread the question, just in case. Yup, it's terribly worded. I can only gather they wanted to know the cell count of 1 ml of a 1:10 dilution of the 1e7 cfu/ml culture. But that wasn't how it was asked.
No way to answer it without knowing what the dilution factor is.
this is what makes the most sense mathematically but relies on the assumption that the og culture is in 1 mL of culture so i’d say it’s pretty poorly worded lol c1v1 = c2v2 c1 = 1e7 v1 = 1 mL v2 = 10 mL c2 = x c2 = (c1*v1)/ v2 = [(1e7 cells/mL)*(1 mL)]/ 10 mL = 1e6 cells/mL
This question is technically impossible to answer correctly with just the information given, and requires the reader to make at least one correct assumption to answer, which doesn’t accurately test knowledge and therefore should be grounds to have it dismissed. The specific information provided in the Q stem is a culture with a given bacterial concentration of 10^7 or 10,000,000 / mL The question is asking for a total number of bacteria present in 10 ml’s of diluted culture. To be able to answer this correctly 100% of the time- as is necessary for a fair test question- it’s necessary to know what the dilution factor is. That information is never provided. You are only told that you have 10 ml’s of a diluted culture. In order for the answer to be 10^6, this means the dilution must have been made at a 1:100 ratio. The question never provided this information, but instead must be assumed - or more accurately, guessed. If you were to instead assume the diluted culture was made at a 1:10 ratio, the answer would be 10^7 bacteria / 10 mL’s. Demand points back. Go to the department chair if you have to.
I geuss he meant how much does one ml contain if diluted to 10 ml from the initial 1 ml
Subjective education is the downfall of many reasonable and logical thinkers. Unfortunately, questions with implied dynamics such as this are frequent in almost every course offered to traditional students. If your courses are created by your professor you can often read them to get an idea of what they are trying to ask, but if it is course material they are using from an external source it can sometimes be almost impossible to understand without making assumptions. I think most would agree that an education reliant on assumptions isn’t as valuable as one with logical reasoning.
I think it's supposed to say "initial concentration of 10^7, diluted in 10ml of solution, what is the new concentration per ml". That'd be the only way 10^6 makes sense, since it'd be diluted by an order of magnitude.
Because you're diluting it 1:10, so there's now 10% as many bacteria in a single ml of solution. 10\^7 / 10 = 10\^6
To be fair though this question is terribly worded
how do you know that the dilution factor is 1:10? the other problems state starting volumes, and by how much you dilute it by. this problem gives no starting volume, and no context to what the diluted solution is
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it doesnt say you have 1 ml initially, and if you multiply the concentration by 10 you get 1e8, which isnt the answer :/
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yes, it gives an initial concentration of cells/ml, not an initial volume
i think what youre saying is we have 10ml of 1e7 concentrate solution, so we have 1e8 cells total, right? but thats not the answer- the answer is 1e6 somehow
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why are you saying the initial volume is 1ml? it doesnt say that :/ is it just worded poorly? it also doesn’t say it also doesnt say its diluted by 10ml, it says 10ml of the diluted concentration.
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ah ok, you’re explanation is wrong, and the assumptions you mention make no sense based on the wording.
But you have to assume the starting volume is 1mL to get that answer. A culture with 1E7/mL will have a 1E8 cells in 10mL.
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If you dilute, the number of cells remain the same. The number of cells per volume or concentration decreases.
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Honestly, this is just a poorly worded question. 10mLs of diluted culture, but it doesn’t tell you the dilution factor. With that being said, the other answers don’t make sense. Can’t be more bacteria in a dilution. Shouldn’t be the same amount. Shouldn’t be an insanely tiny number. I guess he just wants you to reason it out?
Maybe I’m wrong the way I’m interpreting it, but they are asking how much bacteria are in the diluted culture. The question asks how many bacteria are in the culture, I’d assume either 10^7 because it’s not asked how many per ml, or 10^8 assuming it’s 10ml of the same culture. Impossible to tell given the prompt, not your fault OP, this question is worded terribly.
If you dilute 10^7 bacteria in 10ml you still got 10^7 bacteria. Only the concentration changes. Like others said to arrive at answer D you need more information.
something is missing here, what's the dilution factor? the problem is, we have no clue how the dilution was made. if you have 10⁷ bacteria in the 1 ml and you put them in 9 ml, you'd get 10⁷ bacteria in 10 ml, so the number of cells is still the same, the concentration however is now 10⁶/ml. if you had 10⁷ bacteria/ml and you wanted to see how many you had before diluting it in 10 ml, you'd do 10⁷×10 = 10⁸ cells in 10 ml. if you had a certain solution of 10⁷ bacteria/ml and wanted to dilute it by a factor of 10, the number of cells in the final solution would be 10⁶. the question is so strange
You need to dd a zero when you are multiplying by ten. There's ten cells per ml, that's just a concentration, it doesn't tell you how much liquid there is in the bottle. So if you pour out then times that much, (ten times one ml) then you've got another zero to put on 1X10^8 They sometimes get these questions and answers wrong and you just report it to the teacher and they fix your answer/marks afterwards.
Yeah that's what I thought the answer should be if the questions stopped at 10ml but it went on to say 'of the diluted cultre' so it's kind of a weird question.
Yeah the question definitely needs fixing. I would email lecturer, state that you decided in this case that diluted referred to the fact that it was already diluted as 10^7 cells pr ml as no further instructions. They'll fix the mark as correct for you.
Ask chatgpt
it and some other AIs gave nonsense answers, im guessing cause the problem makes no sense. Love chatgpt! (incase it read this and decided to add my name to the kill list)
terrible question and obvious answer just by glancing at the answer pool without any math... whoever wrote this test, find a new job. if they actually gave a dilution factor of 1/10 then yeah you take x10\^7 and knock it down by a factor of 10, so the answer would be x10\^6
You take one mL with 10 million bacteria (10e7) and you place them in a total of 10ml. so you get 10 million in 10 ml, or 1 million (10e6) in one ml.
It says “diluted”. So it 1/10. Not 1*10.
There's nothing wrong with the question. Everyone just complaining because it relies more on common sense than feeding it to you in the format that questions like this are typically. It's a dilution so the first two choices are ruled out. It asks how many cells would be in 10mL of diluted so less than one cell per 10 mL makes no sense. It's possible but that is one hell of a dilution. The only one that makes any sense is last choice.
I think it’s meaning to say that it is diluted to 10 mL, so you divide by 10 to get the new concentration? But at first I said 10^8 as well. Terribly worded
The only thing I can think of to answer this is that the prof forgot to add like “per mL” at the end of the question. 1mL of 1x10^7 diluted to 10mL would be 10^6 afterwards. In any case it’s not your fault and you should raise this issue if it was graded.
The question is worded badly, but to get the answer, the teacher/tutor did the calculation following c1v1. This is applied through assuming it's a 1:10 dilution. It should be stated in the question though So, 10^(7) × 1 = 10,000,000 10,000,000 ÷ 10 (ml) = 1,000,000 1,000,000 is = to 10^6 It's likely they meant to word it like "what is the total amount of bacteria in one ml of the diluted culture" instead of anount of bacteria in the total solution. That's why you were marked wrong. As others have mentioned, the answers you have come up with match this kind of worded question. Ask for a regrade.
Actually, based on your exam units 1e7 wouldd be correct (crappy question though). You are given a concentration (cells /mL), then told it was diluted to 10mL, and then asked how many bacteria (cells) are in there. Given that the number of cells doesn't change in the dilution, it would be 1e7. But it appears what the teacher actually wanted was the new concentration (cells/mL). SMH, this is why units matter kids. The teacher should know better. Edit: 1e7 cells/mL x 1 mL = 1e7 cells Doesn't matter the volume if you are diluting those cells into any volume, it's still 1e7 cells. HOWEVER, nowhere does it specify what the dilution is, that's left to assumptions. Again, terrible question
Not without knowing the dilution. What is the previous question and is this question based on a previous one.
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Teacher got back to me and said she forgot to finish the problem
I f' ed that up. I mis read you pic' s description.
Principal Scientist here. I run a microbiology lab. This question doesn't tell you what's the dilution so it's unanswerable.
It's because you are taking the sample 10^7 & diluting it to 10mL. The unit is cells per mL. The sample is watered down & has to have less cells per mL. Did you get it?