So since kamu is informal and saya is formal, why are they used in one sentence?
kamu could also used in formal, but often use in conversation not in newspaper or educational text. Anda only used in formal situation, wether it is writing or speaking. you could also use kamu in formal way you speak to collague instead of Anda. but Anda is a more preferable to use when you talking to someone higher position or older than you. it is back to whom you speak. hope you understand what i mean