I sometimes get confused between the two.
Just to remmber the rigid rule, ie:

I am
You/We/They are
He/She/It is

in order to fulfil the so-called correct English grammar requirement.
I'm intrigued, what do you mean by 'so-called correct' grammar?
Teachers: We supply a list of EFL job vacancies
"1.Two plus five is seven.
2.Two plus five are seven. "...........Which one of the sentences is correct?