Procvičování na zahajovací písemnou práci 8. ročník

 $\frac{3}{5}+\frac{1}{4}=\frac{3.4+1.5}{20}=\frac{12+5}{20}=\frac{17}{5}$  

 $\frac{7}{9}-\frac{3}{10}=\frac{7.10-3.9}{90}=\frac{70-27}{90}=\frac{43}{90}$  

 $\frac{12}{5}-\left(\frac{4}{5}+\frac{2}{15}\right)=\frac{12}{5}-\frac{4.3+2}{15}=\frac{12}{5}-\frac{14}{15}=\frac{12.3-14}{15}=\frac{36-14}{15}=\frac{22}{15}$  

 $2.\left(2\frac{1}{4}+1\frac{5}{6}\right)=2.\left(\frac{9}{4}+\frac{11}{6}\right)=2.\left(\frac{9.3+11.2}{12}\right)=2.\ \frac{27+22}{12}=\frac{2}{1}.\frac{49}{12}=\frac{49}{6}$  

 $\frac{18}{25}\ .\ \frac{15}{9}=\frac{2}{5}\ .\ \frac{3}{1}=\frac{6}{5}$  

 $\frac{5}{16}\ :\frac{15}{40}=\frac{5}{16}\ .\ \frac{40}{15}=\frac{1}{4}\ .\ \frac{10}{3}=\frac{10}{12}=\frac{5}{6}$  

 $2\frac{1}{4}\ :\ \frac{3}{16}=\frac{9}{4}\ .\ \frac{16}{3}=\frac{3}{1}\ .\ \frac{4}{1}=12$