Amarble or small sphere, made of stone, is found to have a mass of 3.05g. to find its volume it is placed in a gradulated cylindar that originally contains 10.00ml of water. when the marble is placed in hte gradulated cylindar, the new volume of the water and the marble together is 11.20ml. a: calculate the volume of the marble(be sure to include units) b: calculate the density of the marble.(be sure to include units)

a). 
-- There were 10.00 mL of water in the graduated cylinder originally.
-- After the marble was added to the cylinder and sank, the total volume
of water and marble in the cylinder was  11.20 mL.
-- The extra 1.20 mL that suddenly showed up was the volume of the marble.
-- We can use  1 mL = 1 cm³ .
-- The volume of the marble was  1.20 cm³ .

b).
         Density = (mass) / (volume)
For the marble . . .
         Density = (3.05 g) / (1.20 cm³)  =  2.54  gm/cm³  (rounded)

Iwould say a is accurate