contestada

a water tap fills a tank within 4 hours, at the bottom of the tank
there is a hole for empty. the tank takes one hour to be empty. If the tap and the hole
are turning on together, the tank is fully filled. how long will the tank take to be completely
empty?
(70 min, 80 min, 90 min, 100 min)

Respuesta :

LammettHash

Let V be the volume of the tank. The tap fills the tank at a rate of V/(4 hours), or V/4 per hour. The hole empties the tank at a rate of V per hour. If both the tap and hole work together, the net rate of water flow is V/4 - V or -3V/4 per hour.

Starting with a full tank, the volume v of water at time t is given by the function

v(t) = V + (-3V/4) t

Solve v(t) = 0 to find the time it takes to empty:

V - 3V/4 t = 0

V = 3V/4 t

t = V / (3V/4) = 4/3

So it takes 4/3 hours = 80 minutes to empty a full tank.

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