Номер 985 помогите сразу поставлю спасибо и за ранее спасибо)) Задание:вычеслите...

1) $(\frac{5}{21}+ \frac{2}{15})+ \frac{2}{21}=(\frac{5}{21}+\frac{2}{21})+\frac{2}{15}=\frac{7}{21}+\frac{2}{15}=\frac{1}{3}+\frac{2}{15}=\frac{5}{15}+\frac{2}{15}=\frac{7}{15}$
2) $(\frac{2}{35}+ \frac{3}{28})+\frac{1}{28}= (\frac{1}{28}+ \frac{3}{28})+\frac{2}{35}=\frac{4}{28}+\frac{2}{35}=\frac{1}{7}+\frac{2}{35}=\frac{5}{35}+\frac{2}{35}=\frac{7}{35}=\frac{1}{5}$
3) $(\frac{7}{30}+\frac{8}{45})+( \frac{2}{45}+\frac{1}{30})=(\frac{7}{30}+\frac{1}{30})+( \frac{2}{45}+\frac{8}{45})= \frac{8}{30}+ \frac{10}{45}= \frac{24}{90}+ \frac{20}{90}=\frac{44}{90}=\frac{22}{45}$
4) $(\frac{5}{24}+\frac{11}{60})+(\frac{13}{60}+\frac{1}{24})=(\frac{5}{24}+\frac{1}{24})+(\frac{13}{60}+\frac{11}{60})=\frac{6}{24}+\frac{14}{60}=\frac{1}{4}+\frac{14}{60}=\frac{15}{60}+\frac{14}{60}=\frac{29}{60}$