$$ \dfrac{2}{3} - \dfrac{4}{5} $$
Taking LCM
$$3 |\underline{3,5}$$
$$5 |\underline{1,5}$$
$$|1,1$$
∴LCM of $$3$$ and $$5=15$$
$$ \dfrac{2}{3} - \dfrac{4}{5} = \dfrac{2 \times 5}{3 \times5} - \dfrac{4 \times 3}{5 \times 3}$$
$$ = \dfrac{10 - 12}{15} = \dfrac{-2}{15}$$