Multiplicative Inverse

$x\not\equiv 0$ mod n (n is prime number)
x * y ≡ 1 mod n (y is an MI of mod n)
$y\equiv x^{-1}\mathrm{mod}n$

Note:
x and n have to be coprime i.e. GCD(x, n) = 1

$3\not\equiv 0\mathrm{mod}5$
$3\ast 2\equiv 1\mathrm{mod}5$
$2\equiv 3^{-1}\mathrm{mod}5$ (2 is MI of 3 or 2 is MI of 3 mod 5)