Answer 1

For this one:
print(1.0//.1) # 9.0 ... expecting 10.0

Take the numbers one at a time at 21 float precision digits:
print("{:.21f}".format(1.0))
print("{:.21f}".format(0.1))
1.00000000000000000000 # fine
0.10000000000000000551 # whoops

You can mentally multiply both by 10 so it's:
10.0/1.00...551 = 9 dot something

Two slashes // is floor division and always goes down (I've substituted the Python magic method here):
print("{:.21f}".format(1.0.__floordiv__(0.1)))
== 9 and change....down
9.0

To clarify "down" as less, try math.floor(-7.1):
-8.0

So your negatives, in your other examples:
(-1.0//.1 = -10) like: -10.0/1.000...551
-9.something... down is -10.0

(-1.1//.1 = -12)
-1.10000000000000008881... -11 and change
0.10000000000000000551... 1 and less change

-11 and any change floors down:
-12.0