73.
a)
[tex]\frac{5}{12} -\frac{5}{3} +\frac{1}{6} = \frac{5}{12} -\frac{20}{12} +\frac{2}{12} =\frac{-13}{12}[/tex]

74.
a)

[tex]\frac{12}{6} -\frac{2}{6}+\frac{1}{6} =\frac{11}{6}[/tex]
b)

1+1/2+3/4+5/6
=12/12+6/12+9/12+10/6
=37/12

75.
a) 4/3-(1/2+7/8)=4/3-4/8-7/8
=4/3-11/8
=32/24-33/24
=-1/24
b)
4/3-7/5-(3/5-5/7)=4/3-7/5-3/5-5/7
=-10/5+4/3-4/7
=-10/5+28/21-12/21
=-10/5+16/21
=80/105-210/105
=-130/105 ici tu peux réduire
=26/21