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y x 2/5 =8/21
y= 8/21:2/5
y= 20/21
12/7: y =7/5-2/5
12/7:y = 1
y = 12/7 :1
y= 12/7
\(y\times\dfrac{2}{5}=\dfrac{8}{21}\\ y=\dfrac{8}{21}:\dfrac{2}{5}\\ y=\dfrac{20}{21}\\ \dfrac{12}{7}:y+\dfrac{2}{5}=\dfrac{7}{5}\\ \dfrac{12}{7}:y=\dfrac{7}{5}-\dfrac{2}{5}\\ \dfrac{12}{7}:y=1\\ y=\dfrac{12}{7}:1=\dfrac{12}{7}\)
\(12:y=\frac{3}{4}+\frac{4}{5}\)
\(12:y=\frac{15}{20}+\frac{16}{20}\)
\(12:y=\frac{31}{20}\)
\(y=12:\frac{31}{20}\)
\(y=12x\frac{20}{31}\)
\(y=\frac{240}{31}\)
\(\frac{4}{5}xY=1\)
\(y=1:\frac{4}{5}\)
\(y=1x\frac{5}{4}\)
\(y=\frac{5}{4}\)
\(\frac{37}{63}-y=\frac{1}{7}\)
\(y=\frac{37}{63}-\frac{1}{7}\)
\(y=\frac{37}{63}-\frac{9}{63}\)
\(y=\frac{28}{63}\)
\(y=\frac{4}{9}\)
\(y:\frac{3}{7}=\frac{3}{42}+\frac{5}{7}\)
\(y:\frac{3}{7}=\frac{3}{42}+\frac{30}{42}\)
\(y:\frac{3}{7}=\frac{33}{42}\)
\(y:\frac{3}{7}=\frac{11}{14}\)
\(y=\frac{11}{14}x\frac{3}{7}\)
\(y=\frac{33}{98}\)
\(12:y=\frac{3}{4}+\frac{4}{5}\) \(\frac{37}{63}-y=\frac{1}{7}\)
\(12:y=\frac{31}{20}\) \(y=\frac{37}{63}-\frac{1}{7}\)
\(y=12:\frac{31}{20}\) \(y=\frac{4}{9}\)
\(y=\frac{240}{31}\)
\(\frac{4}{5}\cdot y=1\) \(y:\frac{3}{7}=\frac{3}{42}+\frac{5}{7}\)
\(y=1:\frac{4}{5}\) \(y:\frac{3}{7}=\frac{11}{14}\)
\(y=\frac{5}{4}\) \(y=\frac{11}{14}.\frac{3}{7}\)
\(y=\frac{33}{98}\)
\(\frac{12}{7}xy=\frac{16}{21}\)
\(y=\frac{16}{21}:\frac{12}{7}\)
\(y=\frac{4}{9}\)
4,25 : y = 12-7
4,25: y =5
y = 4,25 : 5 =0,85
\(4,25\div y=12-7=5\)
\(\Leftrightarrow y=4,25\div5=\frac{17}{20}\)