a)

$\frac{1}{2}+1,5=0,5+1,5=2$  

$3,2-1\frac{1}{3}=3\frac{2}{10}-1\frac{1}{3}=3\frac{1}{5}-1\frac{1}{3}=3\frac{3}{15}-1\frac{5}{15}=\left(3\frac{3}{15}+\frac{10}{15}\right)-\left(1\frac{5}{15}+\frac{10}{15}\right)=3\frac{13}{15}-2=1\frac{13}{15}$  

$7,3-4\frac{2}{25}=7,3-4\frac{2\cdot 4}{25\cdot 4}=7,3-4\frac{8}{100}=7,3-4,08=3,22$  

b)

$2,4\cdot \frac{3}{8}=2\frac{4}{10}\cdot \frac{3}{8}=2\frac{2}{5}\cdot \frac{3}{8}=\frac{\sout{12}{}^3}{5}\cdot \frac{3}{\sout{8}{}_2}=\frac{9}{10}=0,9$  

$2\frac{3}{4}:2,75=2\frac{3}{4}:2\frac{75}{100}=2\frac{3}{4}:2\frac{3}{4}=1$