A
!$ \dfrac {3} {4} \, - \, \dfrac {5} {6} \, = \, \dfrac {3 \, \cdot \, 3 \, - \, 5 \, \cdot \, 2} {12} \, = \, \dfrac {9 \, - \, 10} {12} \, = \, \dfrac {1} {2} !$ e !$ \dfrac {9} {8} \, \div \, \dfrac {3} {2} \, = \, \dfrac {9 \, \div \, 3} {8 \, \div \, 2} \, = \, \dfrac {3} {4} !$
B
!$ \dfrac {3} {4} \, - \, \dfrac {5} {6} \, = \, \dfrac {3 \, \cdot \, 6 \, - \, 5 \, \cdot \, 4} {4 \, \cdot \, 6} \, = \, \dfrac {18 \, - \, 20} {24} \, = \, \dfrac {2} {24} !$ e !$ \dfrac {9} {8} \, \div \, \dfrac {3} {2} \, = \, \dfrac {9 \, \cdot \, 2} {8 \, \cdot \, 3} \, = \, \dfrac {18} {24} !$
C
!$ \dfrac {3} {4} \, - \, \dfrac {5} {6} \, = \, \dfrac {3 \, \cdot \, 6 \, - \, 5 \, \cdot \, 4} {4 \, \cdot \, 6} \, = \, \dfrac {18 \, - \, 20} {24} \, = \, \dfrac {-2} {24} !$ e !$ \dfrac {9} {8} \, \div \, \dfrac {3} {2} \, = \, \dfrac {9 \, \div \, 3} {8 \, \div \, 2} \, = \, \dfrac {3} {4} !$
D
!$ \dfrac {3} {4} \, - \, \dfrac {5} {6} \, = \, \dfrac {3 \, \cdot \, 3 \, - \, 5 \, \cdot \, 2} {12} \, = \, \dfrac {9 \, - \, 10} {12} \, = \, \dfrac {-1} {12} !$ e !$ \dfrac {9} {8} \, \div \, \dfrac {3} {2} \, = \, \dfrac {9} {8} \, \cdot \, \dfrac {2} {3} \, = \, \dfrac {11} {11} \, = \, 1 !$
E
!$ \dfrac {3} {4} \, - \, \dfrac {5} {6} \, = \, \dfrac {3 \, \cdot \, 3 \, - \, 5 \, \cdot \, 2} {12} \, = \, \dfrac {9 \, + \, 10} {12} \, = \, \dfrac {19} {12} !$ e !$ \dfrac {9} {8} \, \div \, \dfrac {3} {2} \, = \, \dfrac {9} {8} \, \cdot \, \dfrac {2} {3} \, = \, \dfrac {18} {24} !$
