Chemistry question below?

Question

Given the following densities at 25 C:
magnesium: 1.7 g/cm^3
graphite: 1.8 g/cm^3
iron: 7.9 g/cm^3

A block of iron has a mass of 826 g. What is the mass of a block of magnesium that has the same volume as the block of iron?

Answer 1

Density = mass / volume

You are given both the mass and density of a sample of Iron.
Solving for the volume from the density equation above we get,
volume = mass / density
volume = 826 grams / 7.9 grams per cubic centimeters
volume = 104.6 cm^3

Now we are asked to find the mass of a sample Magnesium which has the same volume as the Iron (the volume we just calculated.
Solving the above density equation for mass we get,
mass = density * volume
mass = 1.7 g/cm^3 * 104.6 cm^3
mass = 177.8 grams

So a 826 gram mass of Iron metal will have a volume of 104.6 cubic centimeters.
A 104.6 cm^3 block of Magnesium metal will have a mass of 177.8 grams.

The density of graphite is irrelevant in answering this question.