Mnożymy liczbe przez licznik ułamka, a mianownik pozostawiamy bez zmian.

$\text{a)}30\cdot \frac{1}{3}=\frac{{\sout{30}}^{10}\cdot 1}{{\sout{3}}^1}=\frac{10}{1}=10$

$\text{b)}4\cdot \frac{1}{12}=\frac{{\sout{4}}^1\cdot 1}{{\sout{12}}^3}=\frac{1}{3}$

$\text{c)}\frac{9}{14}\cdot 6=\frac{9\cdot {\sout{6}}^3}{{\sout{14}}^7}=\frac{27}{7}=3\frac{6}{7}$

$\text{d)}\frac{2}{5}\cdot 10=\frac{2\cdot {\sout{10}}^2}{{\sout{5}}^1}=\frac{4}{1}=4$

$\text{e)}15\cdot \frac{2}{3}=\frac{{\sout{15}}^5\cdot 2}{{\sout{3}}^1}=\frac{10}{1}=10$

$\text{f)}16\cdot \frac{7}{20}=\frac{{\sout{16}}^4\cdot 7}{{\sout{20}}^5}=\frac{28}{5}=5\frac{3}{5}$

$\text{g)}\frac{11}{18}\cdot 24=\frac{11\cdot {\sout{24}}^3}{{\sout{24}}^4}=\frac{33}{4}=8\frac{1}{4}$

$\text{h)}21\cdot \frac{5}{7}=\frac{{\sout{21}}^3\cdot 5}{{\sout{7}}^1}=\frac{15}{1}=15$

$\text{i)}\frac{12}{51}\cdot 34=\frac{12\cdot {\sout{34}}^2}{{\sout{51}}^3}=\frac{24}{3}=8$

$\text{j)}\frac{8}{33}\cdot 121=\frac{8\cdot {\sout{121}}^{11}}{{\sout{33}}^3}=\frac{88}{3}=29\frac{1}{3}$