1000-10=5 how to

Question

how to 1000-10=5

Answer 1

Where did you encounter it?
I think it should be
Converting to decimal we get:
1000=8 and 10=2
so 8-2=6

Answer 2

I guess using x-nor operation we can do it right.
x-nor is if both input are same then it's 1 otherwise it's 0. I. e. 1,1 = 1 and 0, 0 = 1 others 0.

So in this example,
1000
0010
---------
0101 = 5 binary representation

Hope you find the solution :)