If two people are of the same type,then they are either both knights or both liars.
If they are of different types,then one is a knight and one is a liar.
Now, suppose Drew and Mohammad say the following.
Drew: We are of the same type.
Mohammad: We are of different types.
Now, what are each?
If Drew was a knight, Mohammed would have to be one, and thus wouldn't disagree with Drew; he thus lies, and then Mohammed must tell the truth.