The amount of a certain type of drug in the bloodstream t t\,t hours after it has been taken is given by the formula
x=De−18t, x = De^{-\frac{1}{8}t}, x=De−81t,where x x\,x is the amount of the drug in the bloodstream in milligrams and D D\,D is the dose given in milligrams.
A dose of 10 mg of the drug is given. Find the amount of the drug in the bloodstream 5 hours after the dose is given. Give your answer in mg to 3 decimal places.
A second dose of 10 mg is given after 5 hours. Show that the amount of the drug in the bloodstream 1 hour after the second dose is 13.549 mg to 3 decimal places.
No more doses of the drug are given. At time T T\,T hours after the second dose is given, the amount of the drug in the bloodstream is 3 mg. Find the value of TTT.
7 exam-style questions on Edexcel A Level Old Maths Logs. Each one has a worked solution and a mark scheme showing where the marks go.