564:8x7=??????????????????
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8 x 7 + 8 x 123 + 8 x 78
= 8 x ( 7 + 123 + 78 )
= 8 x 208
= 1664
![](https://rs.olm.vn/images/avt/0.png?1311)
Để dưới dạng phân số dễ thấy
\(\frac{49\times320}{7\times8}=7\times40=280\)
- Kudo -
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\(\frac{-5}{8}.\frac{5}{12}+\frac{-5}{8}.\frac{7}{12}+\frac{17}{8}\)
= \(\frac{-5}{8}.\left(\frac{5}{12}+\frac{7}{12}\right)+\frac{17}{8}\)
= \(\frac{-5}{8}.\frac{12}{12}+\frac{17}{8}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{5}{8}\times\dfrac{20}{9}-\dfrac{5}{8}\times\dfrac{7}{9}+1\)
\(=\dfrac{5}{8}\times\left(\dfrac{20}{9}-\dfrac{7}{9}\right)+1\)
\(=\dfrac{5}{8}\times\dfrac{13}{9}+1\)
\(=\dfrac{65}{72}\)
Ta có: \(\dfrac{5}{8}=\dfrac{45}{72}\)
Mà: \(65>45\)
Vậy: \(\dfrac{65}{72}>\dfrac{45}{72}\) hay \(\dfrac{5}{8}\times\dfrac{20}{9}+\dfrac{5}{8}\times\dfrac{7}{9}+1>\dfrac{5}{8}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
6/7x5/8x7/3x7/6x8/5=\(\frac{6x5x7x7x8}{7x8x3x6x5}\)=gút gọn được \(\frac{7}{3}\)
\(\frac{6}{7}\times\frac{5}{8}\times\frac{7}{3}\times\frac{7}{6}\times\frac{8}{5}\)
\(=\frac{6\times5\times7\times7\times8}{7\times8\times3\times6\times5}\)
\(=\)6 x 5 x 7 x 7 x 8 / 7 x 8 x 3 x 6 x 5
\(=\frac{7}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
493,5 nha
=493,5 nha
HT