I have a question about the following statement about entropy:
If a source provides us with a sequence chosen from 4 symbols (say A, C, G, T), then the maximum average information per symbol is 2 bits. If the source provides blocks of 3 of these symbols, then the maximum average information is 6 bits per block.
In the first case, each symbol has probability 1/4 therefore the entropy is 2 bits on average -(4*1/4*log(1/4)). The second case where we are sending blocks of 3 symbols is unclear. What is the meaning of sending block of 3 symbols? Are the symbols always different or could be the same? How do we calculate the entropy of group of symbols from a set?