Réponse:
[tex] \frac{7}{8} + \frac{5}{8} = \frac{7 + 5}{8} = \frac{12}{8 } = \frac{3}{2} [/tex]
[tex] \frac{7}{8} + \frac{ - 5}{8} = \frac{7 - 5}{8} = \frac{2}{8} = \frac{1}{4} [/tex]
[tex] \frac{ - 7}{8} + \frac{12}{8} = \frac{ - 7 + 12}{8} = \frac{5}{8} [/tex]
[tex] \frac{12}{8} - \frac{5}{8} = \frac{12 - 5}{8} = \frac{7}{8} [/tex]
[tex] \frac{7}{9} + \frac{1}{18} = \frac{7 \times 2}{9 \times 2} + \frac{1}{18} = \frac{14 + 1}{18} = \frac{15}{18} = \frac{5}{6} [/tex]
[tex] \frac{3}{10} - \frac{4}{15} = \frac{9 - 8}{30} = \frac{1}{30} [/tex]
[tex] \frac{7}{8} \times \frac{5}{8} = \frac{7 \times 5}{8 \times 8} = \frac{35}{64} [/tex]
[tex] \frac{7}{8} \times \frac{8}{5} = \frac{7 \times 8}{8 \times 5} = \frac{56}{40} = \frac{7}{5} [/tex]
[tex] \frac{7}{8} \div \frac{5}{8} = \frac{7}{8} \times \frac{8}{5} = \frac{7}{5} [/tex]
[tex] \frac{7}{8} \div 14 = \frac{7}{8} \times \frac{1}{14} = \frac{1}{8} \times \frac{1}{2} = \frac{1}{16} [/tex]
[tex]4 \div \frac{8}{5} = 4 \times \frac{5}{8} = \frac{5}{2} [/tex]
Et voilà bon courage
