English Translation
One plus two equals three.
“Ένα δύο μας κάνει τρία.”
It is misleading to think that this is expressing a simple maths equation, it would be said without “μας”. As it is, the sentence is saying something more like “one plus two makes us three”. Perhaps in a metaphorical sense, it could be said when someone is talking about adding another person to a group making it three people?