Mathematical fun

A kids told his mother,  our mathe teacher is somehow confused, he told us yesterday 1+4=5 but today says 2+3=5, I dont understand who is 5 and what is his relation with oder persons?! The mother smiled and said, don't worry darling, all  of the mathe teacher are confused, as I was a student like you our teacher solved a complicate equality and told us x=5 and other times  with more troble showed that x=2,  so I've never understand who is x