-11 mod 10
Thanks Heureka,
I do not know if I will ever get the hang of doing these formally but this is an easy one that you can do in your head.
This is mod 10 so think of a circle like a clock only instead of the numbers going to 12 they only go to 10 and then they start again. Also 10 is really 0.
-11 = -10-1
Start at 0, go 10 places in a negative direction and that gets you back to 0 again.
Now go 1 more place in a negative direction and it puts you one number BEFORE 0.
That number is 9
so -11 mod 10 = 9
Some people call Mod maths, Clock maths !!