# How to find variable as the denominator

Copper has a density of $8.96 \text { gm per }cm^3$. If a cylinder of copper weighing $24.31 g$ is dropped into a graduated cylinder containing $20.00 mL$ of water, what will be the new water level?

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Please don't post in the imperative; for general ettiquette in posting your questions, see meta.math.stackexchange.com/questions/1803/… – Arturo Magidin Apr 12 '11 at 20:00
The graduated cylinder needs to avoid being so wide that the water does not cover the copper (and avoid being so narrow that the copper does not fall down). – Henry Apr 13 '11 at 0:17

You want to find out the volume of the copper based on its mass and density. Recall that $\textrm{mass}=\textrm{density }\cdot\textrm{ volume}$. You have an algebraic equation of this form $$8.96\frac{\textrm{g}}{\textrm{cm}^3}\cdot x\textrm{ cm}^3=24.31\textrm{ g}$$ where the $\textrm{cm}^3$ label cancels on the left. You can then solve how many cubic centimeters of copper have been added to the graduated cylinder. Convert this volume to mL, and you should find your answer.