Обчисліть:5/6-3/4; 9/14+8/21; 2.3/4-1.5/6; 7.5/12-[1.5/8+2.1/24]

$1) \frac{5}{6} - \frac{3}{4} = \frac{5*4}{6*4} - \frac{3*6}{4*6} = \frac{20}{24} - \frac{18}{24} = \frac{2}{24} = \frac{1}{12} \\ \\ 2) \frac{9}{14} + \frac{8}{21} = \frac{9*3}{14*3} + \frac{8*2}{21*2} = \frac{21}{42} + \frac{16}{42} = \frac{37}{42} \\ \\ 3)2 \frac{3}{4} -1 \frac{5}{6} =2 \frac{3*6}{4*6} -1 \frac{5*4}{6*4} =2 \frac{18}{24} -1 \frac{20}{24} =1 \frac{42}{24} - 1\frac{20}{24} = \frac{22}{24} = \\ \\ = \frac{11}{12}$

$4) 7 \frac{5}{12} -(1 \frac{5}{8} +2 \frac{1}{24} ) \\ \\ 1 \frac{5}{8} +2 \frac{1}{24} =1 \frac{15}{24} +2 \frac{1}{24} =3 \frac{16}{24} =3 \frac{2}{3} \\ \\ 7 \frac{5}{12} -3 \frac{2}{3} =7 \frac{5}{12} -3 \frac{8}{12} =6 \frac{17}{12} -3 \frac{8}{12} =3 \frac{9}{12} =3 \frac{3}{4}$