Lead has a density of 11.3 g/cm3 and a mass of 282.5 g. what is its volume?

Well we know that density=mass divided by volume, so let's substitute :)

11.3=282.5/V

Now we know that 282.5 has to be divided by SOMETHING in order to get 11.3.

You can waste time trying every number under the sun, or you can use a little trick I learned in elementary school which is to divide 282.5 by 11.3. This works because it shows how many times 11.3 goes into 282.5 which is the volume of this "piece of" lead. Since 11.3 goes perfectly 25 times into 282.5, the Volume of this "piece of" lead is 25 cm³. :)