# Trying to help my daughter with homework but stuck

exponential decay and finding the value of t when 40 = 80 x 2^-0.015t

To get you started. You can use logarithm rules.
sinsua
28 February 2013
That was my fear. I have had a look at several tutorials and finally the memory came back (yes, I did A Level maths and physics but age plays funny tricks). Because she is only just 14, I was sure that they would not be doing natural logarithms and therefore there was something easy I was missing. Guess not and all this hype about falling standards is crap. Many thanks.
kipps
28 February 2013
There is another way. If you rearrange the equation, you can see that the power of 2 needs to = -1. So 0.015t=1. I'm answering this on my phone but when I get to a computer I'll go into more detail about how I got to that if you'd like. It doesn't require any logarithms.
sinsua
28 February 2013
On a computer now.
sinsua
28 February 2013
sinsua
28 February 2013
therefore
sinsua
28 February 2013
sinsua
28 February 2013
so
sinsua
28 February 2013