Suppose that after 3 hours 70% of the drug remains and also the drug decreases exponentially. How much time elapses until only 15% of the drug remains?

Question

math problem, if you can help me with this question it would be great. Thankyou 

Answer 1

0.7a₀ = a₀e^k(3)

0.7 = e^3k

ln 0.7 = 3k

-0.11889 ≈ k

 

0.15a₀ = a₀e^(-0.11889)t

0.15 = e^-011889t

ln 0.15 = -0.11889t

-1.8971 ≈ -0.11889t

15.9596 ≈ t