I've read a lot here about how modular fractions are valid as long as the denominator is invertible, but they always cause me trouble understing this part:
From the definition of congruence:
$$ a \equiv b \pmod m \iff m \big |a-b $$
And $\frac 1 2\equiv \frac 6 2 \equiv 3 \pmod 5$ So I can say $5$ divides $2,5$?