Answer:
After about 9 minutes.
Step-by-step explanation:
We can write an exponential function to model the decay of Herodium-100.
We are given that it decreases by half every minute.
The standard exponential function is given by:
[tex]f(m)=A(r)^m[/tex]
Where A is the initial amount, r is the rate, and m is the rate (in this case, in minutes).
Mathman initially has 2000 mL of Herodium-100. Therefore, A = 2000.
And since it decreases by half every minute, r = 1/2. Thus:
[tex]\displaystyle f(m)=2000\Big(\frac{1}{2}\Big)^m[/tex]
Mathman needs to rest when the Herodium-100 levels drop to 4 mL. Therefore, we can substitute 4 for f(m) and solve for m:
[tex]\displaystyle 4=2000\Big(\frac{1}{2}\Big)^m[/tex]
Solve for m. Divide both sides by 2000:
[tex]\displaystyle \frac{4}{2000}=\frac{1}{500}=\Big(\frac{1}{2}\Big)^m[/tex]
We can take the natural log of both sides:
[tex]\displaystyle \ln\Big(\frac{1}{500}\Big)=\ln\Big(\frac{1}{2}^m\Big)[/tex]
By logarithm properties:
[tex]\displaystyle \ln\Big(\frac{1}{500}\Big)=m\ln\Big(\frac{1}{2}\Big)[/tex]
Therefore:
[tex]\displaystyle m=\frac{\ln(1/500)}{\ln(1/2)}\approx 8.9657\approx 9\text{ minutes}[/tex]
Mathman will have to rest and replenish after 9 minutes.
