A Solution of NaOH had a concentration of 40g/dm3. What mass of NaOH would there be in 250cm3 of the solution?

The two volumes in this question are in different units, so first we need to get both our volumes on the same page. remember 10cm = 1dm so 1000cm³ = 1dm³ (10³cm³ = 1³dm³)So now the question is "a solution of NaOH had a concentration of 40g/1000cm³ . what mass of NaOH would there in 250cm³ of the solution. Now we've set up a ratio. Because we know the concentration of the solution should remain constant, the ratio of the masses and volumes should remain constant as well. 250cm³/1000cm³ = 1/4. 1/4 * 40 = 10g NaOH