Must 1 + 1 always = 2 ?

No, not necessarily so.
1 + 1 can be = 10 (binary calculation)

No. If you combine 1 cubic meter of fine sand with 1 cubic meter of course aggregate, you will get less than 2 cubic meters of mixture. In that particular instance 1 + 1 is less than 2.

In binary, 1 + 1 = 10.

In math, 1 is defined as the starting natural number.
+ 1 gives you the successor
2 is the successor to 1
So 1+1 always = 2.
You can change the base but the meaning stays the same:
one plus one is two.

2 yes

no 1+1 can be 11
such as
0+0=00

1 + 1 in addition modulo 2 is actually equal to zero.

1 + 1 = 2 in the base 10 system only.

1+1=2 yes always 2

1 is a figure.
(1) If used in Decimal system, then 1+1 ALWAYS equals 2.
(2) If used in Binary system, then 1+1 equals 10.
(3) If used in Digital Logic system, then (a) For AND gate 1+1 equals 1. Here the PLUS (+) sign stands in sense of AND Operation, and (b) For OR gate also 1+1 equals 1. But here the PLUS (+) sign stands in sense of OR Operation.

yup.

the answer for 1 + 1 will depend on the base in which 1 is and also the subject in which 1 is being used. For example in biology 1 sperm + 1 egg is not equall to 2 but equal to 1 fertilised egg. If the base is 10, then the answer will be equal to 2

YES

Not always so

No it could be 11also

Yes. But Binary Language According 1+1= 10

Yes

yes