I'm having a problem with a question
The question is: A chemical plant discharges D units of chemical molecules into a river each week. At the end of the week 90% of the chemical molecules have dissipated.
a) Find the number of units of the molecule after n weeks: I got this
an=D+.01(an-1) or an=a1+.01(an-1)
b) Estimate the amount of the molecule in the river for a very long time.
I know it involves the series of what I found in part a but how do I write that.
c) If the toxic level of the molecule is T units, how large an amount of the molecule can the plant discharge each week?
I don't know what do here.
Any ideas will help, Thanks