Question

A certain population of fruit flies which demonstrates exponential growth is 200 flies after 10 days. If the initial population was 15 flies, then what will be the population after 3 weeks?

Answer 1

@sleepyhead314

Answer 2

@Kainui could you give a little help here? :/
I'm thinking something like x + 200 = x*e^(10r)
where x is initial and r is rate
but idk if that's the right idea or where to go from there

Answer 3

Awesome, you're on the right track. But you're trying to solve the general case, which is tougher and actually I don't think you can even solve equations like a+x=e^(x) in terms of elementary functions haha.

Notice they don't say that the population increases by 200 every 10 days. In fact, if it did, then it would be a linear growth, not exponential. In the drug problem they said the concentration changed by decreasing by half after every interval of time which is actually a little different. So really you can just use this!

200 = 15*e^(10r)

Since this is still the same population of flies, you can use the same initial population for both calculations, pretty handy, eh? =)

Answer 4

oh cool! :D
so we can use that to solve for r then? great! thank you! :)

Answer 5

so @jeffsours
plug in 200 = 15*e^(10x) into wolframalpha :P

then copy paste what you get
15*e^(3*7*(paste)) and into wolframalpha again

Answer 6

0.25903

Answer 7

yep that's the first part :)
then do 15*e^(3*7*(0.25903))

Answer 8

3455.35?

Answer 9

that's what I got ^_^ :P
idk if it's right or anything though...

Answer 10

thanks both of you <3