A rectangular tank has a base that is 15 centimeters by 10 centimeters and a height
of 30 centimeters. If the tank is one-third full of water, by how many centimeters will the water level rise if 750 cubic centimeters are poured into the tank?

The correct answer is 5
Explanation: Start by finding the volume of the full tank by multiplying the dimensions together: 15 x 10 x 30 = 4500. If the tank is 1/3 full, then that means it currently includes 1/3 of 4500 cubic centimeters, or 1500 cubic centimeters of water. This would mean the water rises 1/3 of 30 centimeters, meaning the water currently has a height of 10 centimeters. When 750 cubic centimeters of water are added, the tank will be 2250 cubic centimeters full. 2250 is half of 4500, so the tank will be half full. That means the water will rise half the height of the tank, or half of 30 centimeters: 15 centimeters. The question asks for how much the additional water will make the tank rise. Since it rose from 10 centimeters in height to 15, the answer is 5.