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a,
\(y:\dfrac{2}{5}=12\)
\(y=12\times\dfrac{2}{5}\)
\(y=\dfrac{24}{5}=4,8\)
b,
\(\dfrac{11}{10}+\dfrac{4}{5}\times\dfrac{3}{4}=\dfrac{11}{10}+\dfrac{12}{20}=\dfrac{22}{20}+\dfrac{12}{20}=\dfrac{34}{20}=\dfrac{17}{10}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(12:y=\frac{3}{4}+\frac{4}{5}\)
\(12:y=\frac{15}{20}+\frac{16}{20}\)
\(12:y=\frac{31}{20}\)
\(y=12:\frac{31}{20}\)
\(y=12x\frac{20}{31}\)
\(y=\frac{240}{31}\)
\(\frac{4}{5}xY=1\)
\(y=1:\frac{4}{5}\)
\(y=1x\frac{5}{4}\)
\(y=\frac{5}{4}\)
\(\frac{37}{63}-y=\frac{1}{7}\)
\(y=\frac{37}{63}-\frac{1}{7}\)
\(y=\frac{37}{63}-\frac{9}{63}\)
\(y=\frac{28}{63}\)
\(y=\frac{4}{9}\)
\(y:\frac{3}{7}=\frac{3}{42}+\frac{5}{7}\)
\(y:\frac{3}{7}=\frac{3}{42}+\frac{30}{42}\)
\(y:\frac{3}{7}=\frac{33}{42}\)
\(y:\frac{3}{7}=\frac{11}{14}\)
\(y=\frac{11}{14}x\frac{3}{7}\)
\(y=\frac{33}{98}\)
\(12:y=\frac{3}{4}+\frac{4}{5}\) \(\frac{37}{63}-y=\frac{1}{7}\)
\(12:y=\frac{31}{20}\) \(y=\frac{37}{63}-\frac{1}{7}\)
\(y=12:\frac{31}{20}\) \(y=\frac{4}{9}\)
\(y=\frac{240}{31}\)
\(\frac{4}{5}\cdot y=1\) \(y:\frac{3}{7}=\frac{3}{42}+\frac{5}{7}\)
\(y=1:\frac{4}{5}\) \(y:\frac{3}{7}=\frac{11}{14}\)
\(y=\frac{5}{4}\) \(y=\frac{11}{14}.\frac{3}{7}\)
\(y=\frac{33}{98}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Đề đúng phải như này
\(\dfrac{3}{7}\) < y < \(\dfrac{4}{7}\)
\(\dfrac{3}{7}\) = \(\dfrac{3\times5}{7\times5}\) = \(\dfrac{15}{35}\) \(\dfrac{4}{7}\) = \(\dfrac{4\times5}{7\times5}\) = \(\dfrac{20}{35}\)
Bốn phân số thỏa mãn đề bài lần lượt là:
\(\dfrac{16}{35}\); \(\dfrac{17}{35}\); \(\dfrac{18}{35}\); \(\dfrac{19}{35}\)
\(\dfrac{3}{7}=\dfrac{30}{70};\dfrac{4}{7}=\dfrac{40}{70}\)
=> 4 giá trị thỏa mãn là: \(\dfrac{31}{70};\dfrac{33}{70};\dfrac{37}{70};\dfrac{39}{70}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(y\times\frac{3}{5}+y\times\frac{2}{7}=\frac{31}{70}\)
\(\Leftrightarrow y\times\left(\frac{3}{5}+\frac{2}{7}\right)=\frac{31}{70}\)
\(\Leftrightarrow y\times\frac{31}{35}=\frac{31}{70}\)
\(\Leftrightarrow y=\frac{1}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(y=\dfrac{5}{3}-\left(\dfrac{7}{12}:\dfrac{5}{6}\right)=\dfrac{5}{3}-\dfrac{7}{10}=\dfrac{50}{30}-\dfrac{21}{30}=\dfrac{29}{30}\)
b)\(y=\dfrac{4}{15}:\left[\left(\dfrac{4}{5}+\dfrac{1}{2}\right)\times\dfrac{4}{13}\right]=\dfrac{4}{15}:\left[\left(\dfrac{8}{10}+\dfrac{5}{10}\right)\times\dfrac{4}{13}\right]\)
\(y=\dfrac{4}{15}:\left[\dfrac{13}{10}\times\dfrac{4}{13}\right]=\dfrac{4}{15}:\dfrac{2}{5}=\dfrac{2}{3}\)
y-3/4= 5/12:10/3 y-3/4 =5/12*3/10 y -3/4=1/8 y=1/8+3/4 y=7/8