Ice Diamond Riddle SOLUTION ft. Vsauce's Michael Stevens

No this is totally wrong 

The water level BEFORE equals to the amount of water currently in the glass + the percentage of the volume the ice cube with the diamond in it that's below the water level. This percentage CANNOT be more than 100%. If it's 100% that means the ice cube is completely under water and the question says that it floats. Even if the diamond weighed 1000kg that would simply mean 100% of the ice gets added to the water level. In that case the volume would be the same.

Now when the full ice cube melts, the total water level equals to the original water + 100% of the total volume of the ice cube with the diamond in it. Because the entirity of the cube has turned into water (of roughly equal volume. Because ice expands when colder. But so does water when it gets warmer than about 4°C the volume is slightly different. Since we don't know the temperatures of both the ice and the water and the difference is very minimal anyway, we can neglect this). And the diamond is in the water too. Which adds the total up to exactly 100%. Which is definitely more than the volume of the water with the floating ice cube no matter the circumstances