/sci/ - Science & Math

/sci/ I saw this posted here like a month ago, but I can't figure all these out.
Can someone explain 1,3,4,5, and 11 please?
also, on 5, why isn't it 1/2? From my (incredibly) limited knowledge of modulus, I would think that 7 goes into 1/2 0 times, with a remainder of 1/2, so it would be 1/2. Do mods work differently if a<1? Am I just a dumbass? The only experience I have with mods was during a one semester intro to software engineering, and that was barely anything.