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\(\frac{5}{24}\times\frac{5}{12}\times24=\frac{25}{288}\times24=\frac{600}{288}=\frac{25}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{9\cdot10}+\frac{2}{10\cdot12}+\frac{3}{12\cdot15}+\frac{4}{15\cdot19}+\frac{5}{19\cdot24}+\frac{6}{24\cdot30}
\)
\(=\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{15}+\frac{1}{15}-\frac{1}{19}+\frac{1}{19}-\frac{1}{24}+\frac{1}{24}-\frac{1}{30}\)
\(=\frac{1}{9}-\frac{1}{30}\)
\(=\frac{10}{90}-\frac{3}{90}\)
\(=\frac{7}{90}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(12\cdot56+24+42\cdot12\)
\(=12\cdot56+42\cdot12+12\cdot2\)
\(=12\cdot\left(56+42+2\right)\)
\(=12\cdot100\)
\(=1200\)
![](https://rs.olm.vn/images/avt/0.png?1311)
cách 1 . \(\frac{5}{24}\times\frac{5}{12}\times24=\frac{5}{24}\times\left(\frac{5}{12}\times24\right)=\frac{5}{24}\times10=\frac{25}{12}\)
cách 2: \(\frac{5}{24}\times\frac{5}{12}\times24=\frac{5}{12}\times\left(\frac{5}{24}\times24\right)=\frac{5}{12}\times5=\frac{25}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
= 1274 + 2
=1276
HT
1274 + 2
= 1276