I am in a class that is training for becoming a pharmacy technician, really, it is only focused on getting us to pass the test. Last night, I was hit by something that confused me and a couple of other students in conversions, specifically kilograms to grams, and I am hoping someone here may know what is going on, because I don't. I will try to keep this as simple as possible here.

For the purposes of the equation: 1 kg = 2.2 lbs and 1 lb = 454 g

The question involved converting kilograms to grams, and she told us this was how to do it:

(1.3 kg/1)(2.2 lb/1 kg)(454 g/1 lb)=1298 g

According to her, this is how it is supposed to be done, which makes ABSOLUTELY no sense to me. Can anyone explain where she might be getting this from?

I ask here, because there seems to be enough intelligent people here and I've no one else to ask atm.

UPDATE: I spoke to her last night, and because the class is a night class, and she teaches right after getting off of work as a pharmacy tech, what happened was when one of the students and I were asking about it, she believed we were asking something else, so her responses made little to no sense for our questions, and we were tired because we didn't realize she was trying to answer something else. The math problems were on the board the way they were because she was not really correcting class as we were doing the problems together and the students apparently call out the first thing they see in their books, rather take a second and use their brains.

TLDR: It was all a big misunderstanding!

10 years ago*

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It makes sense if you use sig figs. 1.3 has 2 sig figs, 1300 does as well. The lb/kg and g/lb conversions are likely just there to ensure accuracy.

10 years ago
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Yes, the math makes sense, but there is no reason for the extra conversion. The metric system is there for the simplicity of the different measurements it uses. My problem involves why would we both to convert back and forth insuring inaccuracy of the conversion?

10 years ago
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It doesn't... talking about significant figures how would your teacher rationalize going from 2 to 4 significant figures? She just pulled 2 orders of magnitude worth of precision out of her arse.
An answer like 1.3*10^3 g would be more correct, that's why we have scientific notation. I'd get my ass kicked if I just made up significant figures after measuring.
What's going on is that she's giving you the ratios between lb/kg and lb/g and ignoring the fact that kg and g are part of the same damn SI system and by definition related. I guess she doesn't want to blow your minds by throwing the imperial system out the window or something... /shrug
Unless there's some convention specific to pharmacists this is definitely not how it's supposed to be done, simply how she wants you to do it. Check a textbook or something, I know nothing about pharmacy but I know my SI units. :P

10 years ago
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The problem isn't about significant figures, the problems is why am I converting kilograms, to pounds, just to convert it back to grams? The conversion factors are what are supplied to us.

10 years ago
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She's trying to make it intuitive to someone used to working with imperial units. Making it harder by trying to make it easier.
My comment about significant figures was more related to Pohotu3's comment.

10 years ago
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That is dumb, everything in American healthcare is metric. I think the teacher is just lazy or stupid for putting false limitations on what the student can use. So long as a student shows their work and gets the right answer, let them convert it how they want, that is how it works in the real world, which is what they are suppose to be prepping students for.

10 years ago
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kilograms to grams? But 1 kilogram is always 1000 grams...

10 years ago
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When converting from kg to oz, we appearently have to go kg>lb>g>oz as well, which is just as bad.

10 years ago
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Hmmmmm so hard not to make fun of America right now... can I at least make fun of the imperial system? :P

10 years ago
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Your teacher is a moron.

I'm a pharmacist and I would never teach my techs how to do it that way.

Goto youtube and search for "dimensional analysis" and watch the first few videos.

Then check out this page: http://www.alysion.org/dimensional/fun.htm and follow along and do the problems.

If you can follow that page and successfully do the problems, plus memorize metric/standard conversions, that is probably 3/4 of the math on the tech exam. Good luck.

10 years ago
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I am really good with math, so the ability isn't what worries me. I never had the greatest confidence in my teacher, from the moment I spotted the tongue stud.

10 years ago
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The crack head teacher is making the problem purposefully more complicated. This false increase in complexity does nothing to teach students. If you want more complex problems, just use more complex real world examples. Here is a fun one for you:

Patient Doe is 5'3" and 145 pounds. Doctor wants to treat with Drug X, which is dosed at 5mg/kg/day, but in 4 divided doses. The drug must be infused over thirty minutes, and the standard concentration of the drug is 5mg/mL.

What should the flow rate (mL/hr) be for each infusion?

To get credit you must show your work.

10 years ago
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what kind of convertion is that?
just convert everything to Kilograms, and from there to grams.

the "(2.2 lb/1 kg)(454 g/1 lb)" is useless, you are multiplaying by 1... also somehow you lost 2 grams in the last result.

10 years ago
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rounding error..

or that you are not supposed to use 1kg = 1000g because it wasn't given.

EDIT: by rounding error I mean the you are losing accuracy from the not precise conversion from kg -> lb -> g

10 years ago
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That is my whole point!

10 years ago
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Yup, botching the rounding, because number of digits provided for kg -> lbs is lower than it should be. Normal people who follow the International System of Units rules use 2.20462.
There's a reason why those rules have large numbers of digits in the conversion rates, that way they avoid most rounding issues if you're following the rules of significant numbers.

10 years ago
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That and I see no reason as to why I am supposed to convert it to a different measurement system, to convert back to the original measurement system.

10 years ago
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Ugh I'm having a lot of trouble trying to understand what you were actually given?
Because 1kg = 1000g and it looks like you were given 1.3 kg which obviously equals 1300 grams.

1298 grams makes sense because your doing so much rounding, but its sort of like making a sandwich, punching yourself in the face, and then eating the sandwich. Yeah in the end you end up eating your sandwich but I could probably do without the middle part :P.

Thats if what I understand is right though, I haven't slept in aaggges so I'm sorta out of it.

Also seems like 1kg is I guess more closer to 2.205lb which is probably your rounding issue Kg to lb

10 years ago
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Basically this.
I assume it's just important to get the right answer at the end.

On a side note, why do you have to use the metric system anyway? So you in the US use the metric system in science/engineering etc. but in general for most "normal" situations the imperial system is used? I always wondered how unknown the metric system is in the US.

10 years ago
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Healthcare in the US uses metric for most everything except height and weight. And even those we convert to metric for many formulas.

10 years ago
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I literally do not know what to say right now.. 'Murica..

10 years ago
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I would flat-out refuse to do things her way, as she is both making a huge mistake in using only 2.2 as the ratio of lb:kg instead of the full number it really is, as well as needlessly complicating conversion to, I don't know, perhaps make some concept she herself has trouble grasping more clear to her students? There is literally no reason, not one, at all, to do things this way, and it's only confusing as hell and just.. I don't even have any words to finish that sentence. This is so blindingly moronic, that I can only say, I stand by how I began this comment. Screw her bullshit, and demand an explanation for why she is doing things this way, what she is trying to teach by doing things this way, and why she apparently doesn't care about the completely incorrect answer her sum gives - 1.3 kg = 1298 g - or thinks the lessons she's teaching (if she can even articulate a proper response) is more important than giving out false equations. If she can't give you a good reason that she can explain in a way you understand, rebel, refuse her ways.

10 years ago
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Closed 10 years ago by crazyalan1988.