$\dfrac{2^3 . 3^4}{2^2 . 3^2.5}$ = $\dfrac{2 . 3^2}{5}$ = $\dfrac{18}{5}$
$\dfrac{2^4.5^2.11^2.7}{2^3.5^3.7^2.11}$ = $\dfrac{2 . 11}{5.7}$ = $\dfrac{22}{35}$
$\dfrac{121 . 75.130.169}{39 .60.11.198}$ = $\dfrac{11 . 75 . 13 . 169}{39.6.198}$ = $\dfrac{4225 . 143}{396 . 39}$ = $\dfrac{604175}{15444}$
$\dfrac{1998.1990+3978}{1992.1991-3984}$ = $\dfrac{397998}{3962088}$