The initial water level in a 10 -ml graduated cylinder reads 4.1 ml . after a ruby gemstone is dropped into the cylinder , the water level reads 7.1 ml what is the volume of the ruby ?

The volume of water = 4.1 mL
The volume of water + the volume of the ruby gemstone = 7.1 mL

The volume of the ruby gemstone can be calculated as:
7.1 mL - 4.1 mL = 3.0 mL

This is the common procedure to determine volumes of irregular bodies. The body is dropped into water, with previously known volume. The difference in the volume after and before addition of the body is the volume of it.