Question 1096997: The half-life of zulus is 14 days and they decay exponentially. If Angela begins with 20 zulus, how long will it take until only 5 remain?
Found 3 solutions by jorel1380, ikleyn, greenestamps:
Answer by jorel1380(3719)   (Show Source):
You can put this solution on YOUR website! The formula for exponential decay here is P(t)=P(0)e^-kt, where P(t) is the resultant population,P(0)is the initial population, k is the decay constant, and t is the time. So, in the case of half-life, P(t)/P(0)=.5, and t here is 14 days. So:
.5=e^-14k
ln 0.5=ln e^-14k=-14k ln e=-14k
k=0.04951051289713895067265943724701
For there to be 5 zulus left, we have:
5/20=e^-0.04951051289713895067265943724701t
.25=e^-0.04951051289713895067265943724701t
ln 0.25=ln e^-0.04951051289713895067265943724701t=-0.04951051289713895067265943724701t (ln e)=-0.04951051289713895067265943724701t
t=ln 0.25/-0.04951051289713895067265943724701=28 days
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Answer by ikleyn(52781)  (Show Source):
You can put this solution on YOUR website! .
In 14 days only half of initial 20 zulus will remain, i.e. 10 zulus will remain
In the next 14 says only half of these 10 zulus will remain, i.e. 5 zulus will remain.
Answer. In 14 + 14 = 28 days.
Answer by greenestamps(13200)  (Show Source):
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