a. 3 + $\frac{5}{2}$ = $\frac{3}{1}$ + $\frac{5}{2}$ = $\frac{6}{2}$ + $\frac{5}{2}$ = $\frac{11}{2}$
b. 4 -$\frac{5}{7}$ = $\frac{4}{1}$ - $\frac{5}{7}$ = $\frac{28}{7}$ - $\frac{5}{7}$ = $\frac{23}{7}$
c. 1 - ($\frac{2}{5}$ + $\frac{1}{3}$) = 1 - ($\frac{6}{15}$ + $\frac{5}{15}$) = 1 - $\frac{11}{15}$ = $\frac{4}{15}$