During the West African Ebola crisis that started in 2014, geneticists were working to trace the spread of the disease. To do so, they acquired DNA samples of the viruses from a number of patients,...

During the West African Ebola crisis that started in 2014, geneticists were working to trace the spread of the disease. To do so, they acquired DNA samples of the viruses from a number of patients, and affixed a unique “tag” to each patient’s sample.2 A tag is a sequence of 8 nucleotides—each an element of 2 Richard Preston. The Ebola wars. The New Yorker, 27 October 2014. {A, C, G, T}—attached to the end of a virus sample from each patient, so that subsequently it will be easy to identify the patient associated with a particular sample. How many different such tags are there?