[tex] \frac{3}{7} + \frac{5}{11} + \frac{12}{21} + \frac{43}{77} = \\ (factorul \: comun \: e \: 231) \\ \frac{99}{231} + \frac{105}{231} + \frac{132}{231} + \frac{129}{231} = \\ \frac{99 + 105 + 132 + 129}{231} = \frac{465}{231} = \frac{155}{77} [/tex]
