You said "aap kaise ho" but shouldn't aap be paired with hai, and tum with ho?: aap kaise hai tum kaise ho Or is it just slang/not a strict rule?

According to rule… 1st)..Subject “ap” We can use it in formal or informal way. But most of time word Ap use for formal way but ap can fulfill both conditions. Example. Formal..(ap kesy hain) Informal…(ap kesy ho) 2)..Subject “Tum” just use for informal way. Example. Tum kesy ho. Thanks for asking good question. I hope you are clear about this question now, if you still confuse. Let me know. Asking questions and Replying is good trait and tactics to learn language! Regards. Muhammad Atif