any math/chemistry whizzes out there?

im not sure where else to put this so im justting putting in a blog
anyways, i have a chemistry exam tomorrow. im pretty much ready, however im getting confused

i like to think im pretty good at math, but im confused.
we have an equation for density
density = mass/volume
d=m/v

so, i had a question where it was asking to find the volume (we only have this equation to work with, so i just assume i "make it" out of that).

so i thought,
since its d=m/v, i would
(1/m)(d)=(m/v)(1/m)

that would cancel out m and leave v, and add it to the other side. wrong. it gave a wrong answer. so i looked it up, and it really is
m/d=v

what i want to know: why and how?!
im confused at this point. we did not really go over this in class..
any help is appreciated :)

Comments

coolbho3000
You're overthinking this. It's just basic algebra.

Starting out with
d = m/v

Multiply both sides by v
dv = m

Divide both sides by d
v = m/d

Your method works too, but it's a bit more complex.

Starting out with
d = m/v

Divide both sides by m (Multiplying both sides by 1/m is the same as dividing both sides by m)
d/m = (m/v)/m

This equals
d/m = 1/v

Here's where you made the mistake. (m/v)(1/m) equals 1/v, not v.

1/v is the inverse of v, so we can just flip both the fractions.
m/d = v
 
MFDC12
haha thanks guys.
doing dimensional analysis for the past week is throwing me off, haha
 
Hakoda
[quote name='MFDC12' post='3137863' date='Sep 19 2010, 08:53 AM']haha thanks guys.
doing dimensional analysis for the past week is throwing me off, haha[/quote]
I had that stuff last year in Chem, I was good at it but it was so tedious and boring.
 
MFDC12
[quote name='Hakoda' post='3137953' date='Sep 19 2010, 12:14 PM'][quote name='MFDC12' post='3137863' date='Sep 19 2010, 08:53 AM']haha thanks guys.
doing dimensional analysis for the past week is throwing me off, haha[/quote]
I had that stuff last year in Chem, I was good at it but it was so tedious and boring.
[/quote]

i like chemistry for the most part (i also had it in high school). gotta say, still hate sig figs with a passion

also, i like your sig ;D that was from my other blog post haha!
 
Hakoda
[quote name='MFDC12' post='3137984' date='Sep 19 2010, 09:21 AM'][quote name='Hakoda' post='3137953' date='Sep 19 2010, 12:14 PM'][quote name='MFDC12' post='3137863' date='Sep 19 2010, 08:53 AM']haha thanks guys.
doing dimensional analysis for the past week is throwing me off, haha[/quote]
I had that stuff last year in Chem, I was good at it but it was so tedious and boring.
[/quote]

i like chemistry for the most part (i also had it in high school). gotta say, still hate sig figs with a passion

also, i like your sig ;D that was from my other blog post haha!
[/quote]
I agree. I hate sig figs will slow burning rage in my heart. Luckily my school calculator had a specific sig fic calc so it wasn't that bad until I had to do it by hand. I was using a TI-84+ borrowed from the school
 

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