Posted by **Hannah** on Wednesday, August 29, 2012 at 1:55pm.

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??

- Math(Please help, thank you) -
**Steve**, Wednesday, August 29, 2012 at 2:22pm
You got it backwards:

0.12kg is 120g

0.12g = 0.00012kg

.12g * 1kg/1000g = .00012kg

- Math(Please help, thank you) -
**Steve**, Wednesday, August 29, 2012 at 2:24pm
Oops. Forgot to include the volume:

.12g/mm^3 * 1kg/1000g * 1m^3/(1000mm)^3 = 120000kg/m^3

- Math(Please help, thank you) -
**Hannah**, Wednesday, August 29, 2012 at 2:27pm
Oh ok so now to find the percent error do I subtract 120,000 from 7800 and then multiply by 100?

- Math(Please help, thank you) -
**Steve**, Wednesday, August 29, 2012 at 2:35pm
well, if the correct value is 10, and you get 12, then the percent error is (12-10)/10 * 100 = 20%

Yours is figured the same way, but the values are so different, I wonder whether there is something wrong here.

- Math(Please help, thank you) -
**Hannah**, Wednesday, August 29, 2012 at 7:45pm
Yes my data is probably wrong I'm just not sure where I messed up

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