What is the algorithm here?

Question

Algorithms

Please explain how from a=11, b=1, 100 comes out?
It is said that this is the sum in the form of a binary string.

Input: a = "11", b = "1"
Output: "100"

Answer 1

Binary notation	Binary, with zeros	Decimal
eleven	011	3
one	001	one
100	100	4

3 + 1 = 4