Answer
The drug cannot be completely eliminated from one's system.
This is because the kidney removes 25% of the drug, leaving 75% at any time; the 75% of any number will give a smaller number, but never zero.
So, the amount of the drug in the body system can become extremely low, but it can never be 0.
The mathematical proof is shown under explanation.
Step-by-step explanation
We are told that the kidney filters off 25% of the drug out of the system every 4 hours.
This means that 75% of the dosage of the drug remains in the person's system every 4 hours.
If one starts with A₀ of the drug and classify every 4 hour time period as n
At n = 1,
A₁ = 0.75 (A₀)
A₂ = 0.75 (A₁) = 0.75² (A₀)
Aₙ = 0.75ⁿ (A₀)
For this question, we start wit 1000 mg
A₀ = 1000 mg
We are then asked to calculate if Aₙ, the amount of drug in the system after n time periods, can ever be 0
Aₙ = 0.75ⁿ (A₀)
0 = 0.75ⁿ (1000)
To solve for n, if there's an n for when the value of Aₙ = 0, we first divide both sides by 1000
0 = 0.75ⁿ (1000)
0 = 0.75ⁿ
We then take the natural logarithms of both sides
In 0 = In (0.75ⁿ)
In (0.75ⁿ) = In 0
n (In 0.75) = In 0
But, since In 0 does not exist, it shows that there is no value of n that can make the value of Aₙ go to 0.
Hope this Helps!!!