Math(Please help, thank you)
posted by Hannah .
I am trying to calculate my percent error for an experiment conducted. I need to compare my average density calculated to the accepted average density but I am having trouble doing this because of the conversions.
My average density was 0.12 g/mm^3. The accepted value is for iron which is 7.8 X 10^3 kg/m^3.
So to get 0.12 g to kg I multiplied by 1000 and got 120.
Then I subtracted 120 from 7.80 X 10^3.
Is this correct so far??

You got it backwards:
0.12kg is 120g
0.12g = 0.00012kg
.12g * 1kg/1000g = .00012kg 
Oops. Forgot to include the volume:
.12g/mm^3 * 1kg/1000g * 1m^3/(1000mm)^3 = 120000kg/m^3 
Oh ok so now to find the percent error do I subtract 120,000 from 7800 and then multiply by 100?

well, if the correct value is 10, and you get 12, then the percent error is (1210)/10 * 100 = 20%
Yours is figured the same way, but the values are so different, I wonder whether there is something wrong here. 
Yes my data is probably wrong I'm just not sure where I messed up