A party is being held at a local mansion. The host is very rich and his success is because of one thing ~ his famous recipe for Spaghetti!
The only guests that may attend are people the host knows and trusts, whom he gave the password to enter to.
Here's where you come in. You and a friend are trying to steal this recipe. You sneak by and listen to the passwords.
The first guest arrives. The security says "5", and the guest replies "5".
The second guest arrives. The security says "-6", the guest replies "19".
The third guest arrives. The security says "10.5", the guest replies "11".
Your friend thinks he got it all figured out. He approaches the security and as they say "What time do you call this? Your number is -7", when he replies "20" and he's admitted!!!
The fourth guest arrives in a cloud of blue smoke obviously late. After apologizing to security for being late he is challenged with "0" and replies "26" and is admitted.
The fifth guest is hot on his heels and arrives. The guard says "Look mate, the letter of the rules here is that you can't come in after 7.00pm but, you are only 3 minutes late so if you get the correct answer then you can come in." and the challenge is "-3" to which the guest replies "16" and is admitted.
Knowing your time has run out you walk up to security, wishing your friend had told you the secret to get in and get "You are going to be the last guest I admit in this zone. 3.5" before the guard quickly changes his mind and asks you for "-9.5" instead, what is the correct response and how do you figure it out?
Look at what the guards are saying. Some of their words are incongruous and will give you a hint on what to focus on. Note: I am a fluent English speaker (Australian born and raised), so any weird mangling of phrases is totally intentional and is a clue.