[tex]\it a)\ \ \dfrac{^{3)}1}{\ \ 10}\ \ \d s i\ \ \dfrac{^{2)}11}{\ 15} \Rightarrow \dfrac{3}{30}\ \ \d s i\ \ \dfrac{22}{30}\\ \\ \[[10,\ \ 15]=30\\ \\ \\ b)\ \ \dfrac{^{5)}5}{\ \ 12}\ \ \d s i\ \ \dfrac{^{3)}9}{\ 20} \Rightarrow \dfrac{25}{60}\ \ \d s i\ \ \dfrac{27}{60}\\ \\ \[[12,\ \ 20]=60[/tex]
[tex]\it c)\ \ \dfrac{^{3)}7}{\ \ 18}\ \ \d s i\ \ \dfrac{^{2)}8}{\ 27} \Rightarrow \dfrac{21}{54}\ \ \d s i\ \ \dfrac{16}{54}\\ \\ \[[18,\ \ 27]=4[/tex]
