# Math Help - confussion on changing measurements etc

1. ## confussion on changing measurements etc

So I'm working out the volume and have 0.5mm, 10km & 100km.

I've changed 0.5mm into 5.0x10^-6 km

So it works out as 5.0x10^-6 km x 10km x 100km = 5.0x10^-4 km^3

I also need to work out mass using the desity value of 1x10^3 kg m^-3 but do I need to convert any value like I did with the 0.5mm and what would the measurement be in? kg m^-3 x km^3 becomes what?

2. Hi dg2008

0.5 mm is not 5.0x10^-6 km

$0.5 mm = 5 x 10^{-1} mm = 5 x 10^{-1} \;mm * \frac{1 \;km}{10^{6}mm} = ...km$

As for the density:

$1x10^3 kg m^{-3}=1x10^3\frac{kg}{m^3}*\frac{1 m^3}{....km^3} = ....\frac{kg}{km^3}$

3. my mistake I have writen 5x10^-7 down but on here typed it wrong. Prob' worng also.

Density I just don't get at all.

4. Hi dg2008

1 m^3 = .... km^3

Can you figure it out ?

5. 1 m^3 = 0.001 km^3 or 1x10^-3

So then the m^3 & 1m^3 cancel each other out. Thats about as far as I can go lol Is it just 1x10^3 x 1x10^-3?

6. Hi dg2008

Nope. 1 m^3 is not 0.001 km^3

1 m^3 = 1 m * 1 m * 1 m = 0.001 km * 0.001 km * 0.001 km = ....

Then you put the number in the "..." and you're right that the two m^3 will cancel out each other.

7. 1.0 × 10^-9 km^3

8. Originally Posted by dg2008
1.0 × 10^-9 km^3
Yes, that's right

Originally Posted by songoku
Then you put the number in the "..." and you're right that the two m^3 will cancel out each other.
Have you tried it ?

9. So I put 1.0 × 10^-9 km^3 into the first ... then does it become

1x10^3 kg x 1×10^-9 km^3 as the m^3 has be canceled out.

or

1x10^3 kg / 1×10^-9 km^3

10. Hi dg2008

Judging from the equation I wrote, which one is right? km^3 should be at numerator or denominator?

11. I think it's the / not x one I wrote.

Do you know anywhere online where I can write equations correctly?

12. You're right. It's the "/" one

I think you can learn how to write equation here : http://www.mathhelpforum.com/math-he...-tutorial.html

13. yay so:

1x10^3 / 1x10^-9 = 1x10^12 kg km^-3 ?

14. Yups

15. so I have 5.0x10^-4 km^3 as the volume and 1x10^12 kg km^-3 as density but how is mass worked out?

I know its m= d x v but what do I do about the measurements do the km^-3 and km^3 cancel out?