Question

A patient is given a 100-milligram dosage of a drug that decays exponentially at a rate of 11% per hour. Which equation could be used to find the time when 15 milligrams of the drug remain?

A. 100 = 15(0.89)^x
B. 100 = 15(0.11)^x
C. 15 = 100(0.89)^x
D. 15 100(0.11)^x

Answer 1

Exponential functions can be expressed as:

f=ir^t, f=final value, i=initial value, r=rate or common ratio, t=term number or "time" when it is fractional...In this case we have:

f=100((100-11)/100)^x

f=100(0.89)^x and we want to solve for when f=15 so

15=100(0.89)^x