Answer:
51 milligrams
Step-by-step explanation:
Exponential growth or decay can be modeled by the equation ...
y = a·b^(x/c)
where 'a' is the initial value, 'b' is the "growth factor", and 'c' is the time period over which that growth factor applies. The time period units for 'c' and x need to be the same.
In this problem, we're told the initial value is a = 190 mg, and the value decays to 95 mg in 19 hours. This tells us the "growth factor" is ...
b = 95/190 = 1/2
c = 19 hours
Then, for x in hours the remaining amount can be modeled by ...
y = 190·(1/2)^(x/19)
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After 36 hours, we have x=36, so the remaining amount is ...
y = 190·(1/2)^(36/19) ≈ 51.095 . . . . milligrams
About 51 mg will remain after 36 hours.
