Addition et Soustraction de fractions

a) $\dfrac{7}{9} - \dfrac{2}{9} = \dfrac{7-2}{9} = $ $\dfrac{5}{9}$

b) $\dfrac{5}{3} - \dfrac{1}{6} = \dfrac{5 \times 2}{3 \times 2} - \dfrac{1}{6} = \dfrac{10}{6} - \dfrac{1}{6} = \dfrac{9}{6} = $ $\dfrac{3}{2}$

c) $\dfrac{7}{10} - \dfrac{1}{2} = \dfrac{7}{10} - \dfrac{1 \times 5}{2 \times 5} = \dfrac{7}{10} - \dfrac{5}{10} = \dfrac{2}{10} = $ $\dfrac{1}{5}$

d) $\dfrac{9}{4} - \dfrac{3}{8} = \dfrac{9 \times 2}{4 \times 2} - \dfrac{3}{8} = \dfrac{18}{8} - \dfrac{3}{8} = $ $\dfrac{15}{8}$

e) $\dfrac{11}{12} - \dfrac{2}{3} = \dfrac{11}{12} - \dfrac{2 \times 4}{3 \times 4} = \dfrac{11}{12} - \dfrac{8}{12} = \dfrac{3}{12} = $ $\dfrac{1}{4}$

a) $\dfrac{2}{5} + \dfrac{1}{6} = \dfrac{2 \times 6}{5 \times 6} + \dfrac{1 \times 5}{6 \times 5} = \dfrac{12}{30} + \dfrac{5}{30} = $ $\dfrac{17}{30}$

b) $\dfrac{3}{7} + \dfrac{5}{8} = \dfrac{3 \times 8}{7 \times 8} + \dfrac{5 \times 7}{8 \times 7} = \dfrac{24}{56} + \dfrac{35}{56} = $ $\dfrac{59}{56}$

c) $\dfrac{2}{3} + \dfrac{4}{5} = \dfrac{2 \times 5}{3 \times 5} + \dfrac{4 \times 3}{5 \times 3} = \dfrac{10}{15} + \dfrac{12}{15} = $ $\dfrac{22}{15}$

d) $\dfrac{1}{2} + \dfrac{1}{3} = \dfrac{1 \times 3}{2 \times 3} + \dfrac{1 \times 2}{3 \times 2} = \dfrac{3}{6} + \dfrac{2}{6} = $ $\dfrac{5}{6}$

e) $\dfrac{3}{4} + \dfrac{2}{5} = \dfrac{3 \times 5}{4 \times 5} + \dfrac{2 \times 4}{5 \times 4} = \dfrac{15}{20} + \dfrac{8}{20} = $ $\dfrac{23}{20}$

a) $\dfrac{3}{7} - \dfrac{5}{8} = \dfrac{3 \times 8}{7 \times 8} - \dfrac{5 \times 7}{8 \times 7} = \dfrac{24}{56} - \dfrac{35}{56} = $ $- \dfrac{11}{56}$

b) $\dfrac{2}{3} - \dfrac{1}{4} = \dfrac{2 \times 4}{3 \times 4} - \dfrac{1 \times 3}{4 \times 3} = \dfrac{8}{12} - \dfrac{3}{12} = $ $\dfrac{5}{12}$

c) $\dfrac{4}{5} - \dfrac{2}{3} = \dfrac{4 \times 3}{5 \times 3} - \dfrac{2 \times 5}{3 \times 5} = \dfrac{12}{15} - \dfrac{10}{15} = $ $\dfrac{2}{15}$

d) $\dfrac{1}{2} - \dfrac{1}{5} = \dfrac{1 \times 5}{2 \times 5} - \dfrac{1 \times 2}{5 \times 2} = \dfrac{5}{10} - \dfrac{2}{10} = $ $\dfrac{3}{10}$

e) $\dfrac{5}{6} - \dfrac{2}{7} = \dfrac{5 \times 7}{6 \times 7} - \dfrac{2 \times 6}{7 \times 6} = \dfrac{35}{42} - \dfrac{12}{42} = $ $\dfrac{23}{42}$

a) $\dfrac{-7}{15} + \dfrac{-1}{4} = \dfrac{-7 \times 4}{15 \times 4} + \dfrac{-1 \times 15}{4 \times 15} = \dfrac{-28}{60} + \dfrac{-15}{60} = \dfrac{-28 - 15}{60} = $ $\dfrac{-43}{60}$

b) $\dfrac{3}{5} - \dfrac{7}{8} = \dfrac{3 \times 8}{5 \times 8} - \dfrac{7 \times 5}{8 \times 5} = \dfrac{24}{40} - \dfrac{35}{40} = $ $\dfrac{-11}{40}$

c) $\dfrac{1}{2} + \dfrac{-1}{4} = \dfrac{2}{4} + \dfrac{-1}{4} = \dfrac{2-1}{4} = $ $\dfrac{1}{4}$

d) $-\dfrac{2}{3} + \dfrac{3}{4} = \dfrac{-2 \times 4}{3 \times 4} + \dfrac{3 \times 3}{4 \times 3} = \dfrac{-8}{12} + \dfrac{9}{12} = $ $\dfrac{1}{12}$

e) $\dfrac{3}{10} - \dfrac{-4}{5} = \dfrac{3}{10} + \dfrac{4}{5} = \dfrac{3}{10} + \dfrac{4 \times 2}{5 \times 2} = \dfrac{3}{10} + \dfrac{8}{10} = $ $\dfrac{11}{10}$