$\dfrac{25}{50}$ = $\dfrac{25:25}{50:25}$=$\dfrac{1}{2}$
$\dfrac{15}{120}$ = $\dfrac{15:15}{120:8}$=$\dfrac{1}{8}$
$\dfrac{64}{720}$ = $\dfrac{64:16}{720:16}$ = $\dfrac{4}{45}$
$\dfrac{5}{25}$ = $\dfrac{5:5}{25:5}$ = $\dfrac{1}{5}$
$\dfrac{36}{48}$ = $\dfrac{36:12}{48:12}$ = $\dfrac{3}{4}$
$\dfrac{84}{126}$ = $\dfrac{84:42}{126:42}$ = $\dfrac{2}{3}$