Question

11) The Half-Life of Tylenol is approximately 3 hours.
If you take 1000mg, how Tylenol much is left in your body after 4 hours?

Answer 1

The quantity remaining, r, from an initial quantity of r0 with a half life of h is given at time t by:
r=r0*e^-t*ln(2)/h

For the given case,
initial quantity = 1000
half life, h = 3 hours
time lapse, t = 4 hours
so
r = 1000e^-4ln(2)/3 mg

I'll let you finish the calculations because my calculator does not have the ln(x) function.

As a check of the formula, you can calculate the quantity left after 3 hours. It should be 500 mg.