An adult takes 400mg of ibuprofen. Each hour, the amount of ibuprofen in the person's

system decreases by 29%. If 100mg of ibuprofen is left, how much time has passed? Use

A = Pert

4.048 hours

Step-by-step explanation:

A = Pe^ (rt)

After 1 hour, the amount decreases by 29% (A = 0.71P), so r is:

0.71P = Pe^ (r*1)

0.71 = e^r

r = ln (0.71)

r = - 0.342

P = 400. When A = 100, the time t is:

100 = 400e^ (-0.342 t)

0.25 = e^ (-0.342 t)

ln (0.25) = - 0.342 t

t = - ln (0.25) / 0.342

t ≈ 4.048

Approximately 4.048 hours have passed.