Answer
$\dfrac{1}{y^2}$
Work Step by Step
Using the laws of exponents, the given expression, $
\dfrac{(y^2)^5}{(y^3)^4}
,$ simplifies to
\begin{array}{l}\require{cancel}
\dfrac{y^{2(5)}}{y^{3(4)}}
\\\\=
\dfrac{y^{10}}{y^{12}}
\\\\=
y^{10-12}
\\\\=
y^{-2}
\\\\=
\dfrac{1}{y^2}
.\end{array}