# Math Help - half life

1. ## half life

The amount of ibuprofen in an adult's bloodstream decreases at an hourly rate of 27%, and a normal dose is 400 mg.

What is the half life of ibuprofen?

2. You've been given a data point for the decay equation, $A\, =\, Pe^{rt}$; namely, (t, A) = (1, 0.73), where t is in hours. And they've given you the value of P; namely, 400.

So plug the values they've given you into the equation they've given you, and solve for the decay rate r. Then plug in "200" for A (that is, half of P), and solve for the time t.