a. $\frac{5}{24}\times \frac{5}{12}\times 24$

C1: $\frac{5}{24}\times \frac{5}{12}\times 24=\left (  \frac{5}{24}\times \frac{5}{12}\right )\times 24=\frac{25}{288}\times \frac{24}{1}=\frac{600}{288}$

C2: $\frac{5}{24}\times \frac{5}{12}\times 24=\frac{5}{24}\times \left (  \frac{5}{12}\times \frac{24}{1}\right )=\frac{5}{24}\times \frac{120}{12}=\frac{600}{288}$

b. $\left ( \frac{1}{4}+ \frac{2}{3} \right )\times \frac{4}{5}$

C1: $\left ( \frac{1}{4}+ \frac{2}{3} \right )\times \frac{4}{5}=\left ( \frac{3}{12}+\frac{8}{12} \right )\times \frac{4}{5}=\frac{11}{12}\times \frac{4}{5}=\frac{44}{60}$

C2: $\left ( \frac{1}{4}+ \frac{2}{3} \right )\times \frac{4}{5}=\frac{1}{4}\times \frac{4}{5}+\frac{2}{3}\times \frac{4}{5}=\frac{4}{20}+\frac{8}{15}=\frac{12}{60}+\frac{32}{60}=\frac{44}{60}$

c. $\frac{3}{7}\times \frac{16}{33}+\frac{16}{33}\times \frac{4}{7}$

C1: $\frac{3}{7}\times \frac{16}{33}+\frac{16}{33}\times \frac{4}{7}=\frac{48}{231}+\frac{64}{231}=\frac{112}{231}$

C2: $\frac{3}{7}\times \frac{16}{33}+\frac{16}{33}\times \frac{4}{7}=\left ( \frac{3}{7}+\frac{4}{7} \right )\times \frac{16}{33}=\frac{7}{7}\times \frac{16}{33}=\frac{112}{231}$