(Solved): 2.35 In pulse-code modulation (PCM), a PCM word consists of a sequence of binary digits (bits) of ...

$$2.35$$ In pulse-code modulation (PCM), a PCM word consists of a sequence of binary digits (bits) of $$1\mathrm{s}$$ and $$0\mathrm{s}$$. (a) Suppose the PCM word length is $$n$$ bits long. How many distinct words are there? (b) If each PCM word, three bits long, is equally likely to occur, what is the probability of a word with exactly two 1s to occur?