Lets assume that the volume of ice is V m^3 and the volume inside water is v m^3.
The density of water should be 1000kg/m^3
Here what happens is that due to mass of ice it sinks in.But due to upthrust the weight of the ice is held at equilibrium.Upthrust is generated by the displaced mass of water due to the volume of ice inside water.
So at equilibrium;
Weight of ice = upthrust of water
We know mass = volume * density
V*900 = v*1000
v/V = 0.9 = 90%
So 90% or 9/10 fraction of the volume is inside the water.Only 10% or 1/10 fraction of volume is at outside the water.