You are Here: Home >< Maths

# C4 question expotential growth and decay

Announcements Posted on
Four hours left to win £100 of Amazon vouchers!! Don't miss out! Take our short survey to enter 24-10-2016
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

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

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

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

Posted from TSR Mobile
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!

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 31, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Who is getting a uni offer this half term?

Find out which unis are hot off the mark here

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams