View Full Version : Applications of exponential/logarithmic functions
sim0nz12345
Aug 3, 2007, 04:20 AM
Hi there could you please help me with this question
The population of bees in a bee-hive after (n) days is given by P(n)=5000 x 3^(n/40).Find
a) how long it takes for the population to treble,
b) how lone it will take for the population to increase by 20%
Thanks
Capuchin
Aug 3, 2007, 04:30 AM
First we work out what the population is at day 0, plugging 0 in for n we find P(0) is 5000. Now we can set up our equations:
a) solve 5000*3^{\frac{n}{40}} = 5000*3
b) solve 5000*3^{\frac{n}{40}} = 5000*1.2
Do you need help solving these?
sim0nz12345
Aug 3, 2007, 06:09 AM
Yes please
It would be much appreciated if you could show me ow to solve it
Thanks
Capuchin
Aug 3, 2007, 08:57 AM
ill show you the first one.
cancel 5000 from both sides and we have:
3^{\frac{n}{40}} = 3
Take ln of both sides:
ln(3^{\frac{n}{40}}) = ln(3)
Apply basic log rule ln(x^a) = aln(x):
\frac{n}{40}ln(3) = ln(3)
cancel ln(3) from both sides:
\frac{n}{40} = 1
n = 40.
Now you try the next one.
sim0nz12345
Aug 3, 2007, 05:32 PM
Cool thanks
But why is it 1.2 in b), was it formed from the 20%
Capuchin
Aug 4, 2007, 12:21 AM
Yup 0.2 is the 20% but you want to keep the 100% that you have already so it's 1.2