Bonjour,
[tex]A=\frac{7}{4}-\frac{2}{5} *\frac{7}{8} =\frac{7*10}{4*10} -\frac{2*7}{5*8} =\frac{70}{40} -\frac{14}{40} =\frac{70-14}{40} =\frac{56}{40} =\frac{7*8}{5*8} =\frac{7}{5} \\\\\\B=\frac{15}{16} : \frac{9}{4} +\frac{1}{12} =\frac{15}{16} *\frac{4}{9} +\frac{1}{12} =\frac{15*4}{16*9} +\frac{1}{12} =\frac{60}{144} +\frac{1}{12} =\frac{12*5}{12*12} +\frac{1}{12} =\frac{5}{12} +\frac{1}{12} =\frac{5+1}{12} =\frac{6}{12} =\frac{6*1}{6*2} =\frac{1}{2}[/tex]
