a) \(\frac{5}{12}+\frac{5}{20}+\frac{5}{30}+...+\frac{5}{9900}\)
b) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
c) \(\frac{7}{6}+\frac{13}{12}+\frac{21}{20}+...+\frac{91}{90}\)
d) \(\left(6-\frac{2}{3}+\frac{1}{2}\right)-\left(5+\frac{5}{3}-\frac{2}{3}\right)-\left(3-\frac{7}{3}+\frac{5}{2}\right)\)