´a´ for telling the time

Question

There was a test question that said ´8 a 10´ means the same thing as ´8 menos 10´ but this guide doesn´t mention it.Are they interchangeable?

Accepted Answer

Hola Ryan
I'm not sure where you saw "8 a 10" meaning the same as "8 menos 10". 
When we use "menos" that could be either talking about "time", as in:

Son las 8 menos 10. 
It's ten to eight.

Or, in mathematics: "minus"

8 menos 10 es -2  (8-10 = -2 ) 
8 minus 10 equals -2

Used with "a" however, we would use it to say "from... till...":

Yo solo trabajo dos horas por la mañana, de 8 a 10.
I only work two hours in the morning, from 8 till 10.

So, they are used differently.
If you remember where you saw it in our site, please send a screenshot or a link and we'll have another look.
Saludos
Inma