How many 5-element DNA sequences

a) end with A?

b) start with T and end with G?

c) contain only A and T?

d) do not contain C?

Hint: Recall that a DNA sequence is a sequence of letters, each of which is one of A, C, G, or T. Thus by the product

rule there are 4^5 = 1024 DNA sequences of length five if we impose no restrictions.

discrete math

discrete structures