How do we observe in experiments?

Alarge marble is dropped in a graduated cylinder with 35ml of water in it. the water level increases to 49ml. what is the volume of the marble

How can a give a full method for the experiment of separating sand from water by filtration? 1-materials 2-steps 3-conclusion also for water and salt separated by the evaporation or distillation process

When the mercury level in a barometer decreases that atmospheric pressure has