Math prep
posted by Britt .
1). Using the function: y=y0,(.90)^t1. In this equation y0 is the amount of initial dose and y is the amount of medication still available t hours after drug is administered. Suppose 20mg of the drug is administered. How long will it take for this initial dose to reach 50mg?
2).a contractor needs $80000.00 to finish one of the biuldings. He is able to borrow at 10% per year compounded quarterly. how much will interest amount to if he pays off the loan in 5 years?
the y0 should actually be y with a little 0 at the bottom right corner and as i said from the equation it is the amount of initial dose. Plus the initial dose is 200mg not 20 sorry. so how long would it take to get from 200mg to 50mg?

As I mentioned the last time you posted this question, what is the purpose of the comma after the y0?
You did not answer that question, so I will just ignore the comma.
y = y0 (.9)^^(t1)
50 = 200 (.9)^(t1)
.25 = (.9)^(t1)
ln .25 = (t1) ln.9
t1 = ln.25/ln.9 = 13.16
t = 14.16 hrs 
I had answered the second part of your question before.
http://www.jiskha.com/display.cgi?id=1353294829