Compound Interest Problem?
An endangered species of fish has a population that is decreasing exponentially. The populations 5 years ago was 1900. Today, only 1100 fish are alive. Once the population drops to 100, the situation will be irreversible. When will this happen?

Question

Compound Interest Problem? 
An endangered species of fish has a population that is decreasing exponentially. The populations 5 years ago was 1900. Today, only 1100 fish are alive. Once the population drops to 100, the situation will be irreversible. When will this happen?

kc_kennylau · Answer

let its rate constant be r.
$$1900*e^{-5r}=1100$$
$$r=0.1093$$
let the time be t.
$$1100*e^{-0.1093t}=100$$
$$t=21.93\approx22$$

kc_kennylau · Answer

add back the units by yourself :)

kc_kennylau · Answer

@desiretoinspirecindy

anonymous · Answer

Sorry, I had went off my computer .. but THANKS! I got that answer eventually, I was a little confused, but now you just confirmed it was right! THANKS!!

kc_kennylau · Answer

no problem :)
(i was sleeping lolz)