text: help on 8'th grade science homework? a graduated clinder contains 50ml of water. after adding a 30g rock the water in the cylinder reads 75 ml. what is the density of the rock?  any advice/help? density = mass / volume  since the volume increases 25 ml, we know the volume of the rocks is 25 ml.  and since we know the rocks weigh 30 g, we can find the density.  d = 30 / 25 = 1.2 g/ml