Prin operatia de derivare a proportiilor, se pot obtine alte proportii, plecand de la o proportie data.
[tex]\it\dfrac{4}{8} =\dfrac{1}{2} \Longrightarrow \dfrac{4}{1} =\dfrac{8}{2} \\ (am\ schimbat \ mezii\ intre\ ei)[/tex]
[tex]\it\dfrac{4}{8} =\dfrac{1}{2} \Longrightarrow \dfrac{8}{4} =\dfrac{2}{1} \\ (am\ inversat \ rapoartele ) [/tex]
[tex]\it\dfrac{4}{8} =\dfrac{1}{2} \Longrightarrow \dfrac{4+8}{8} =\dfrac{1+2}{2} \Longrightarrow \dfrac{12}{8} = \dfrac{3}{2} \\ (am\ adunat\ la \ numarator\ numitorul) [/tex]
