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A fish tank initially has 4kg of salt dissolved in 100L of water.
It is decided that this concentration is too high! So, fresh water is mixed at a rate of 10L/mind, while 10L of mixture is removed per minute.
If x kg/L is the concentration of the saltwater solution in the tank t seconds after the fresh water is first added, find the differential equation for x.
I thought dx/dt = -10x
But i got the answer wrong
water remains constant at 100L. Only salt concentration changing with time
So concentration = 100x?
i think it will be dx/dt = 4 - 0.4t
sorry 100 dx/dt = 4 - 0.4t
I got the solution, it says 10dx/dt + x = 0
But i dont know how they got that
maybe it's like this : salt concentration is being reduced by 10 X / 100 L where x is salt concentration and water remains constant so only changing thing is 10 L of solution being removed