A graduated cylinder has a mass of 50 g when empty. When 30 mL of water is added, the graduated cylinder has a mass of 120 g. If a rock is added to the graduated cylinder, the water level rises to 75 mL and the total mass is now 250 g. What is the density of the rock? 

2.9g/cm^3

Explanation:

We're given that the mass of the system before the rock was added was  

120g . The mass after the rock was added was  250g, so the rock's mass is 130g.

The initial volume of water in the graduated cylinder was  

30 mL , and the volume after the rock was added read  75mL , so the rock's volume is 45mL

Density = Mass over Volume.

AKA. 130g/45mL

2.9g/cm^3 (rounded)

1.43 x 10^-11 j the guy commented the awnser just making sure u see it .

it is the most commonly accepted one