Question 153128
Remember, 


1 kg = 1000 g or 1 kg = 1*10^3 g


and 


1 km = 1000 m = 100,000 cm  or  1 km = 1*10^3 m = 1*10^5 cm



So 1,200,000,000 kg = 1,200,000,000,000 g or 1,200,000,000 kg = 1.2*10^12 g 



and 1 km^3 = (100,000)*(100,000)*(100,000) cm^3 = 1,000,000,000,000,000 cm^3 = 1*10^15 cm^3



-----------------------------


So 


1,200,000,000 kg = 1.2*10^12 g 


and 


1 km^3 = 1*10^15 cm^3



----------------------------------


Also, remember that


<pre> 
            Mass
Density =  ---------
            Volume

</pre>


which is symbolically 


{{{D=M/V}}}





{{{D=M/V}}} Start with the given equation.




{{{D=(1.2*10^12)/(1*10^15)}}} Plug in the given mass M=1.2*10^12 g and the given volume V=1*10^15 cm^3 



{{{D=1.2*10^(12-15)}}} Divide 1.2 by 1 to get 1.2. Divide {{{10^12}}} by {{{10^15}}} by subtracting



{{{D=1.2*10^(-3)}}} Subtract the exponents.



So the density is {{{1.2*10^(-3)}}} g/cm^3