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![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(2,54+6,3\cdot\left(-1.25\right)\)
\(=2.54-7,875\)
=-5,335
b: \(\dfrac{1}{5}\cdot\dfrac{4}{7}+\dfrac{3}{7}\cdot\dfrac{1}{5}-\dfrac{1}{5}\)
\(=\dfrac{1}{5}\left(\dfrac{4}{7}+\dfrac{3}{7}\right)-\dfrac{1}{5}\)
\(=\dfrac{1}{5}-\dfrac{1}{5}=0\)
c: \(\dfrac{-10}{13}+\dfrac{5}{17}-\dfrac{3}{13}+\dfrac{12}{17}-\dfrac{11}{20}\)
\(=\left(-\dfrac{10}{13}-\dfrac{3}{13}\right)+\left(\dfrac{5}{17}+\dfrac{12}{17}\right)-\dfrac{11}{20}\)
\(=-1+1-\dfrac{11}{20}=-\dfrac{11}{20}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta lay 72 * 135 duoc 9720
Roi ta lay 9 * 28 *15 duoc 3780
Ta cong 9720 va 3780 duoc 13500
Ta lay 13500 / 25 duoc 540
Ta lay 3500 / 25 duoc 140
Cuoi cung ta lay 540 - 140 bang 400
nhu vay ket qua la 400
ban doc xong nho ket ban voi minh nhe
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(5^{19}\div5^{17}+3\right)\div7\)
\(=\left(5^2+3\right)\div7\)
\(=\left(25+3\right)\div7\)
\(=28\div7=4\)
\(\left(5^{19}:5^{17}+3\right):7\)
\(=\left(5^2+3\right):7\)
\(=\left(25+3\right):7\)
\(=28:7\)
\(=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
b: \(=\dfrac{2}{7}-\dfrac{3}{7}\cdot\dfrac{-2}{3}=\dfrac{2}{7}+\dfrac{2}{7}=\dfrac{4}{7}\)
c: \(=\dfrac{3}{7}-\dfrac{7}{2}-\dfrac{3}{7}+\dfrac{7}{2}=0\)
Câu 1: C
Câu 2: A
Câu 3: D
Câu 4: C
Câu 5: D
1C 2 A 3 D 4 C 5 D