Among the following oxides Cr₂O₃, V₂O₅, FeO, Mn₂O₇, ZnO, Cu₂O, MnO₂, CrO₃, NiO

If x = number of basic oxides

y = number of acidic oxides

z = number of amphoteric oxides

then the value of $\frac{\left(x+y\right)}{z}$  is