Density of a certain solid is 5.23×10−6kg/mm3. convert this density into kilograms per cubic meters.

 In a laboratory, you determine that the density of a certain solid is 5.23×10−6kg/mm3. Convert this density into kilograms per cubic meter. 
... 
5.23×10^−6 kg/mm3 x 1000 mm^3/cm^3 x 1000 cm^3/dm^3 

x 1000 dm^3/m^3 = 5230 kg/m^3. 

notice how all the units cancel out but the required.