Binary subtraction

basic decimal subtraction

Example

		3	4	16
	3	3	5	6	4
	2	3	4	9	0
_	_	_	_	_	_
	1	0	0	7	4

4 - 0 = 4
Borrow 1 to make 16 - 9 = 7
Borrow to make 4 - 4 = 0
Borrow to make 3 - 3 = 0
3 - 2 = 1

Answer 10074

Onto binary subtraction

The four basic subtraction rules

0 - 0 = 0
1 - 0 = 1
1 - 1 = 0
10 - 1 = 1

	0	1	10	10
	1	0	1	0	1
		1	1	1	0
_	_	_	_	_	_
	0	0	1	1	1

1 - 0 = 1
Borrow 1 to make 10 - 1 = 1
Borrow 1 to make 10 - 1 = 1
Borrow 1 to make 1 - 1 = 0
Borrow 0 to make 0

You can double check

10101 = 21
1110 = 14
21 - 14 = 7
Answer 111 = 7