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The volume of a rock will vary depending on the size of the rock. Since a rock is an irregularly shaped object, a good way to determine its volume is by using water displacement. When an object is placed in water, the amount of water that is displaced by the object is equal to the volume of the object. 

Example:

  1. Fill a graduated cylinder with 30 mL of water. 30 mL is the initial volume of the water.
  2. Carefully place a rock in the water. You will notice that the level of water in the graduated cylinder increases. Let's say that the water level increases to 50 mL when the rock is added. 50 mL is the final volume of the water.
  3. To find the volume of the rock, subtract the initial volume of the water from the final volume of the water: 50 mL - 30 mL = 20 mL. Therefore, the volume of the rock would be equal to 20 mL or 20 cc.
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