Chapter 5.2, Problem 128E

[T] A certain drug is effective for an average patient only if there is at least I mg per kg in the patient’s system, while it is safe only if there is at most 2 mg per kg in an average patient’s system. Suppose that the amount in a patient’s system diminishes by a multiplicative factor of 0.9 each hour after a dose is administered. Find the maximum interval N of hours between doses, and corresponding dose range d (in mg/kg) for this N that will enable use of the drug to be both safe and effective in the long term.