When does 1 plus 1 plus 1 equal 1

Are you serious?

If you're in (mod 1) or (mod 2). :)

1 + 1(0) = 1

That's all I can think of.

In Boolean algebra or logic functions - basically a true statement plus a true statement is a true satement. In this type of algebra 0 = false and 1 = true, so:

0+0 = 0
1+0 = 0
0+1 = 0
1+1= 1