Question

Percy is filling a cylindrical tank with water. The tank is

9 meters high and has a base area of 78 square meters.
The hose he is using fills the tank at a rate of 6 cubic
meters in one minute. How long will it take Percy to fill
the tank?
A. 13 min
B. 117 min
C. 52 min
D. 468 min

Answer 1

Volume of water in the tank:

Differentiate both sides with respect to time t :

V changes at a rate of 2000 cc/min (cubic cm per minute); use this to solve for dh/dt :

(The question asks how the height changes at the exact moment the height is 50 cm, but this info is a red herring because the rate of change is constant.)

Answer 2

B

Explanation:

78x9=702

702/6=117 minutes.