$\text{a)}3a+1\frac{3}{4}=2\frac{1}{5}$

$3a=2\frac{1}{5}-1\frac{3}{4}$

$3a=2\frac{4}{20}-1\frac{15}{20}$

$3a=\frac{9}{20}$

$a=\frac{9}{20}:3$

$a=\frac{{\sout{9}}^3}{20}\cdot \frac{1}{{\sout{3}}^1}$

$a=\frac{3}{20}$  


sprawdzenie:

$3\cdot \frac{3}{20}+1\frac{3}{4}=\frac{9}{20}+1\frac{15}{20}=1\frac{24}{20}=2\frac{4}{20}=2\frac{1}{5}$  

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$\text{b)}1\frac{2}{3}-5c=1\frac{1}{4}$

$5c=1\frac{2}{3}-1\frac{1}{4}$

$5c=1\frac{8}{12}-1\frac{3}{12}$

$5c=\frac{5}{12}$

$c=\frac{5}{12}:5$

$c=\frac{{\sout{5}}^1}{12}\cdot \frac{1}{{\sout{5}}^1}$  

$c=\frac{1}{12}$  


sprawdzenie:

$1\frac{2}{3}-5\cdot \frac{1}{12}=1\frac{2}{3}-\frac{5}{12}=1\frac{8}{12}-\frac{5}{12}=1\frac{3}{12}=1\frac{1}{4}$  

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$\text{c)}\frac{1}{2}p:1\frac{3}{4}=8$

$\frac{1}{2}p=8\cdot 1\frac{3}{4}$

$\frac{1}{2}p={\sout{8}}^2\cdot \frac{7}{{\sout{4}}^1}$

$\frac{1}{2}p=2\cdot 7$

$\frac{1}{2}p=14$  

$p=14\cdot 2$

$p=28$


sprawdzenie:

$\frac{1}{2}\cdot 28:1\frac{3}{4}=14:\frac{7}{4}=14\cdot \frac{4}{7}=2\cdot 4=8$