7.4. On the island, there live knights and liars. Knights always tell the truth, and liars always lie. Some of the inhabitants claimed that there is an even number of knights on the island, while the others claimed that there is an odd number of liars on the island. Is the number of inhabitants on the island even or odd? Don't forget to justify your answer.
Answer: even.

Clearly, if two people made the same statement, then they are either both liars or both knights. Since the island has at least one liar and at least one knight, either all the knights made the first statement and all the liars made the second, or vice versa. In the first case, both the number of knights and the number of liars are even, and in the second case, both are odd. Therefore, the total number of people on the island must be even.