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Q: gasoline is pumped from the tank of a tanker truck at a rate of 20L/s. if the tank is a cylinder 2.5 m in diameter and 15 m long, at what rate is the level of gasoline falling when the gasoline in the tank is 0.5m deep? express in exact answer in cm/min [1L=1000 cm^3]

i did:

dv/dt = - 1200000cm^3/min

dv/dt = dv/dh*dh/dt

Vcylinder = pi r^2 l {l=h=length of the cylinder}

r = 125h/50 cm = 5h/2

V= pi(5/2h)^2l

dv/dh = pi 25/2 hl

-1200000 = pi 25/2 (50)(1500) dh/dt

dh/dt = -96/75 pi

i've got a good feeling that this is wrong. please help.