a, 2$\frac{3}{5}$ + $\frac{3}{4}$
= $\frac{13}{5}$ + $\frac{3}{4}$
= $\frac{52 + 15}{20}$
= $\frac{67}{20}$
b, 3$\frac{1}{3}$ - 2$\frac{4}{5}$
= $\frac{10}{3}$ - $\frac{14}{5}$
= $\frac{50 - 42}{15}$
= $\frac{8}{15}$
c, 1$\frac{7}{8}$ × 2$\frac{2}{5}$
= $\frac{15}{8}$ × $\frac{12}{5}$
= $\frac{15 × 12}{8 × 5}$
= $\frac{180}{40}$
= $\frac{9}{2}$
d, 2$\frac{3}{7}$ : 2$\frac{1}{3}$
= $\frac{17}{7}$ : $\frac{7}{3}$
= $\frac{17 × 3}{7 × 7}$
= $\frac{51}{49}$
