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# C4 question expotential growth and decay watch

1. N = 200e^4t

this is the formula im using,

the question is the number of bacteria (N) in a colony is such that the hourly rate of increase of N is equal to four times the number of bacteria present. Initially there are 200 bacteria present, find the time taken for the number of bacteria to grow to 700 giving your answer to the nearest minute
2. so

dN/dt = 4N.... what can you do next ?
3. (Original post by the bear)
so

dN/dt = 4N.... what can you do next ?
not sure, kinda stuck on what to sub in
4. (Original post by SunDun111)
not sure, kinda stuck on what to sub in
you could maybe integrate it ?
5. (Original post by the bear)
you could maybe integrate it ?
But why.. would I do that ?
6. Can you take a picture of the question?
You might've missed out something

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7. (Original post by sherfyq)
Can you take a picture of the question?
You might've missed out something

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Thats literally all it gives me..
8. I thought youre gonna send a picture of the question

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9. (Original post by sherfyq)
I thought youre gonna send a picture of the question

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I will, i think i missed a bit out, didnt read page b4, it tells me to integrate it, ill send a picture with my working!
10. Looking at the first part of the question (Found it online) the equation seems fine to use. Sub 700 in as the N, then rearrange to get t. First divide by 700, so 200/700 = e^4t. Log both sides to get rid of the e^ part, so ln(700/200)= 4t, t = (ln(7/2))/4. Think that should get the answer, then obviously round it to be the nearest minute.
11. (Original post by VeeDubSpecs)
Looking at the first part of the question (Found it online) the equation seems fine to use. Sub 700 in as the N, then rearrange to get t. First divide by 700, so 200/700 = e^4t. Log both sides to get rid of the e^ part, so ln(700/200)= 4t, t = (ln(7/2))/4. Think that should get the answer, then obviously round it to be the nearest minute.
Thats the same question, but non the worksheet my teacher gave it didnt have the top bit!

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