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![](https://rs.olm.vn/images/avt/0.png?1311)
`@` `\text {Ans}`
`\downarrow`
`a)`
`25,7 + 9,48 + 14,3`
`= (25,7 + 14,3) + 9,48`
`=40 + 9,48`
`= 49,48`
`b)`
`8,24 + 3,69 + 2,31`
`= 8,24 + (3,69 + 2,31)`
`= 8,24 + 6`
`= 14,24`
`c)`
`8,65 + 7,6 + 1,35 + 0,4`
`= (8,65 + 1,35) + (7,6 + 0,4)`
`= 10 + 8`
`= 18`
`d)`
`5,92 + 0,44 + 5,56 + 4,08`
`= (5,92 + 4,08) + (0,44 + 5,56)`
`= 10 + 6`
`= 16`
`e)`
`7,5 + 6,5 + 5,5 + 4,5 + 3,5 + 2,5`
`= (7,5 + 2,5) + (6,5 + 3,5) + (5,5 + 4,5)`
`= 10 + 10 + 10`
`= 30`
`7,`
`a)`
Ta có:
\(42,54 > 42,45; 87,65 > 87,56\)
\(\Rightarrow\) \(42,54+87,65>42,56+87,56\)
`b)`
\(96,38+74,85 = 171,73 \\ 74,38 + 96,85 = 171,23\)
\(\Rightarrow\) \(96,38 + 74,85 = 96,85 + 74,38\)
`c)`
\(8,8 + 6,6 + 4,4 = 8,8 + 11 = 19,8 \\ 9,9 + 5,5 + 7,7 = 23,1\)
`19,8 < 23,1`
\(\Rightarrow\) `8,8 + 6,6 + 4,4 < 9,9 + 5,5 + 7,7`
![](https://rs.olm.vn/images/avt/0.png?1311)
`@` `\text {Ans}`
`\downarrow`
`1)`
\(A=\dfrac{5}{7}+\dfrac{3}{4}+\dfrac{1}{5}+\dfrac{2}{7}+\dfrac{1}{4}\)
`=`\(\left(\dfrac{5}{7}+\dfrac{2}{7}\right)+\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\dfrac{1}{5}\)
`=`\(1+1+\dfrac{1}{5}=\dfrac{11}{5}\)
Vậy, `A=`\(\dfrac{11}{5}\)
`2)`
\(B=4\dfrac{4}{9}\div\dfrac{8}{3}+\dfrac{2}{3}\div2\dfrac{2}{3}\)
`=`\(\dfrac{40}{9}\times\dfrac{3}{8}+\dfrac{2}{3}\times\dfrac{3}{8}\)
`=`\(\dfrac{3}{8}\times\left(\dfrac{40}{9}+\dfrac{2}{3}\right)\)
`=`\(\dfrac{3}{8}\times\dfrac{46}{9}=\dfrac{23}{12}\)
Vậy, `B =`\(\dfrac{23}{12}\)
`3)`
\(C=\dfrac{2}{15}\times\dfrac{13}{27}+\dfrac{2}{15}\times\dfrac{14}{27}\)
`=`\(\dfrac{2}{15}\times\left(\dfrac{13}{27}+\dfrac{14}{27}\right)\)
`=`\(\dfrac{2}{15}\times1=\dfrac{2}{15}\)
Vậy, `C=`\(\dfrac{2}{15}\)
`4)`
\(D=40,35+112,37-18,35+17,63\)
`=`\(\left(40,35-18,35\right)+\left(112,37+17,63\right)\)
`= 22+130`
`= 152`
Vậy, `D = 152.`
![](https://rs.olm.vn/images/avt/0.png?1311)
`@` `\text {Ans}`
`\downarrow`
`3,`
`a)`
\(\dfrac{5}{2}\times\dfrac{1}{3}+\dfrac{1}{4}=\dfrac{5}{6}+\dfrac{1}{4}=\dfrac{13}{12}\)
`b)`
\(\dfrac{6}{5}+\dfrac{3}{5}\div2=\dfrac{6}{5}+\dfrac{3}{10}=\dfrac{3}{2}\)
`c)`
\(\left(\dfrac{6}{15}+\dfrac{3}{15}\right)\times\dfrac{4}{9}=\dfrac{9}{15}\times\dfrac{4}{9}=\dfrac{4}{15}\)
`d)`
\(\dfrac{3}{7}\times\left(\dfrac{9}{11}-\dfrac{2}{11}\right)=\dfrac{3}{7}\times\dfrac{7}{11}=\dfrac{3}{11}\)
`4,`
`a)`
\(\dfrac{3}{7}+\dfrac{4}{9}+\dfrac{4}{7}+\dfrac{5}{9}=\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{7}{7}+\dfrac{9}{9}=1+1=2\)
`b)`
\(\dfrac{1}{5}+\dfrac{4}{11}+\dfrac{4}{5}+\dfrac{7}{11}=\left(\dfrac{1}{5}+\dfrac{4}{5}\right)+\left(\dfrac{4}{11}+\dfrac{7}{11}\right)=\dfrac{5}{5}+\dfrac{11}{11}=1+1=2\)
`c)`
\(\dfrac{1}{15}+\dfrac{4}{15}+\dfrac{5}{18}+\dfrac{7}{18}=\left(\dfrac{1}{15}+\dfrac{4}{15}\right)+\left(\dfrac{5}{18}+\dfrac{7}{18}\right)=\dfrac{1}{3}+\dfrac{2}{3}=1\)
`d)`
\(\dfrac{1}{8}+\dfrac{1}{12}+\dfrac{3}{8}+\dfrac{5}{12}=\left(\dfrac{1}{12}+\dfrac{5}{12}\right)+\left(\dfrac{1}{8}+\dfrac{3}{8}\right)=\dfrac{1}{3}+\dfrac{1}{2}=\dfrac{5}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
`@` `\text {Ans}`
`\downarrow`
`1,`
`a)`
\(\dfrac{7}{19}+\dfrac{12}{19}=\dfrac{7+12}{19}=\dfrac{19}{19}=1\)
`b)`
\(\dfrac{5}{13}+\dfrac{4}{13}=\dfrac{5+4}{13}=\dfrac{9}{13}\)
`c)`
\(\dfrac{24}{11}-\dfrac{13}{11}=\dfrac{24-13}{11}=\dfrac{11}{11}=1\)
`d)`
\(\dfrac{35}{8}-\dfrac{19}{8}=\dfrac{35-19}{8}=\dfrac{16}{8}=2\)
`2,`
`a)`
\(\dfrac{3}{7}+\dfrac{5}{4}=\dfrac{12}{28}+\dfrac{35}{28}=\dfrac{12+35}{28}=\dfrac{47}{28}\)
`b)`
\(\dfrac{4}{5}+\dfrac{12}{10}=\dfrac{8}{10}+\dfrac{12}{10}=\dfrac{8+12}{10}=\dfrac{20}{10}=2\)
`c)`
\(\dfrac{12}{8}-\dfrac{4}{9}=\dfrac{108}{72}-\dfrac{32}{72}=\dfrac{76}{72}=\dfrac{19}{18}\)
`d)`
\(\dfrac{2}{7}-\dfrac{3}{14}=\dfrac{4}{14}-\dfrac{3}{14}=\dfrac{1}{14}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 6: \(\dfrac{40}{7}\) \(\times\) \(\dfrac{14}{5}\) = \(\dfrac{40}{5}\) \(\times\) \(\dfrac{14}{7}\) = 8 \(\times\) 2 = 16
Chọn C.16
Câu 7: 2\(\dfrac{1}{4}\) = \(\dfrac{2\times4+1}{4}\) = \(\dfrac{9}{4}\);
2\(\dfrac{1}{4}\) gấp \(\dfrac{1}{8}\) số lần là: \(\dfrac{9}{4}\) : \(\dfrac{1}{8}\) = 18 (lần)
Chọn B. 18
Câu 8: Chiều rộng của hình chữ nhật là: \(\dfrac{25}{12}\) : \(\dfrac{5}{3}\) = \(\dfrac{5}{4}\) (m)
Chu vi của hình chữ nhật là: ( \(\dfrac{5}{3}\) + \(\dfrac{5}{4}\)) \(\times\) 2 = \(\dfrac{35}{6}\)(m)
\(\dfrac{35}{6}\) m = 5\(\dfrac{5}{6}\) m
Chọn B. 5\(\dfrac{5}{6}\) m
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a.\dfrac{7}{19}+\dfrac{12}{19}=\dfrac{7+12}{19}=\dfrac{19}{19}=1\)
\(b.\dfrac{5}{13}+\dfrac{4}{13}=\dfrac{5+4}{13}=\dfrac{9}{13}\)
\(c.\dfrac{24}{11}-\dfrac{13}{11}=\dfrac{24-13}{11}=\dfrac{11}{11}=1\)
\(d.\dfrac{35}{8}-\dfrac{19}{8}=\dfrac{35-19}{8}=\dfrac{16}{8}=2\)
a,\(\dfrac{7}{19}\)+\(\dfrac{12}{19}\)=\(\dfrac{19}{19}\)=1
b,\(\dfrac{5}{13}\)+\(\dfrac{4}{13}\)=\(\dfrac{9}{13}\)
c,\(\dfrac{24}{11}\)-\(\dfrac{13}{11}\)=\(\dfrac{11}{11}\)=1
d,\(\dfrac{35}{8}\)-\(\dfrac{19}{8}\)=\(\dfrac{16}{8}\)=2
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(\dfrac{4}{12}=\dfrac{1}{3}\)
\(\dfrac{5}{20}=\dfrac{1}{4}\)
\(\dfrac{21}{35}=\dfrac{3}{5}\)
\(\dfrac{17}{34}=\dfrac{1}{2}\)
Vậy \(\dfrac{17}{34}=\dfrac{1}{2}\)
B= {73;74;75:76;77;78;79}
b= {73;74;75:76;77;78;79}