Interchange of interrogative and assertive sentences

When a question is asked for the sake of obtaining admission or denial, the answer should be in the negative when the question is in the affirmative and vice versa. The following examples will illustrate the point.
Question: Aren’t dogs faithful animals?
Here the speaker expects the answer to be ‘yes’. In that case, the statement will be in the affirmative. If the speaker expects the answer to be ‘no’, then the statement will have to be in the negative.
Statement: Dogs are faithful animals.
Question: Will he ever forget that experience?
Statement: He will never forget that experience.
Question: Was she not a stupid to do that?
Statement: She was a stupid to do that.
Question: Can a leopard change its spots?
Statement: A leopard cannot change its spots.
Statement: Everyone would like to be rich.
Question: Who would not like to be rich?
Question: How can man remain immortal?
Statement: Man cannot remain immortal.
Question: Why waste time like this?
Statement: It is foolish to waste time like this.
Questions of this kind are sometimes called rhetorical questions. They do not require an answer but are simply devices by which statements can be expressed in an emphatic manner.
Very often, a rhetorical question is used to draw attention to a negative situation – to the fact that the answer is obviously ‘No’.
‘What is the use of waiting for her?’ (= It is no use waiting for her.)
‘Are we going to let them do this?’ (= We are not going to let them do this.)