PLEASE help
A 25 gram sample of a substance that's used for drug research has a k-value of 0.1229 Find the substance's half-life in days.

Question

PLEASE help 
A 25 gram sample of a substance that's used for drug research has a k-value of 0.1229 Find the substance's half-life in days.

anonymous · Answer

set $$\huge e^{-0.1229t}=0.5$$ and solve for $t$ in two steps

morganwarren · Answer

i have literally no clue what i'm doing

anonymous · Answer

ok then lets go slow

anonymous · Answer

first off, the 25 grams has nothing to do with anything
you are looking for a half life, the time it takes for the substance to be reduces to one half its original amount

anonymous · Answer

*reduced

anonymous · Answer

second the "k value" means the number that goes in the sky for your exponential decay function $$A(t)=
A_0e^{-kt}$$
you seen something like that before?

morganwarren · Answer

No not really I've just been guessing

anonymous · Answer

hmm then you can't really do this problem although it only takes two steps and a calculator

wolf1728 · Answer

e^-.1229*t = .5

Taking logs of both sides
-.1229*t * Log (e) = Log (.5)

e= 2.71828

-.1229*t * 0.4342944818 = -0.3010299957

t = -0.3010299957 / (-.1229 * 0.4342944818)

If you have a calculator you can calculate the answer.

morganwarren · Answer

5.6?

wolf1728 · Answer

Yes, 5.6 is correct