Question

A rectangular prism-shaped water tank has a base $10$ ft by $8$ ft. The tank is filled with water up to a height of $7$ ft. On filling the bottom of the tank with rocks, the water level rises to $8.5$ ft. What is the volume of the rocks?

• A. $320$ cu ft
• B. $160$ cu ft
• C. $180$ cu ft
• D. $120$ cu ft

Answer 1

The correct option is D $120$ cu ft

The volume of the tank when it is filled with water = $V_1=$ (Base area) $\times$ Height $=(10\times 8)\times 7=560$ cu ft

The volume of the tank when it is filled with water and rocks$=V_2=$ (Base area) $\times$ Height $=(10\times 8)\times 8.5=680$ cu ft

Volume of rocks $=$ Volume of water displaced by the rocks

$=V_2-V_1$

$=680-560$

$=120$ cu ft