Brüche/Addition und Subtraktion/Aufgabe

Bringen Sie auf einen Bruchstrich (geschickter Nenner?):

1. ${}{\frac {1}{5}}+{\frac {9}{10}}$
2. ${}{\frac {7}{6}}-{\frac {3}{4}}$
3. ${}2{\frac {3}{4}}-{\frac {7}{7}}$
4. ${}{\frac {2}{3}}+{\frac {7}{12}}-1{\frac {3}{8}}$
5. ${}{\frac {a}{b}}+{\frac {c}{d}}$
6. ${}{\frac {a}{b}}+{\frac {c}{b^{2}}}$
7. ${}{\frac {a}{4bc}}+{\frac {d}{6c^{2}}}$
8. ${}{\frac {a}{b+c}}+{\frac {d}{b-c}}$
9. ${}{\frac {a}{1+x}}+{\frac {b}{1-x}}+{\frac {c}{(1+x)^{2}}}$
10. ${}{\frac {a-b}{c+d}}+{\frac {c-d}{a+b}}$