A radioactive tracer with a half-life of 4.0 h is injected into a patient at 09:00 h. Blood samples are withdrawn at 09:30 h and again at 10:00 h. Each time, exactly 10 % of the tracer still present in the bloodstream is removed with the sample and is not returned.
(i) Calculate the fraction of the original tracer remaining in the patient immediately after the first sample is taken.
(ii) Calculate the fraction of the original tracer remaining immediately after the second sample is taken.
(iii) Express the total activity removed in the two samples as a fraction of the initial activity injected at 09:00 h.