1)-0,8:(-4) và 0,6:3 2) 2(1)/(3):3(1)/(4) và 7:13 3ài 2. L ập tất cả các tỉ lệ thức có thể từ các đẳng thức sau ) 4.15=30.2 2) 5.20=2.50 4) 0,36.4,25=0,9.1,7 3) 15.42=21.30 6) (-0,3):2,7=(-1,7 5) -0,8cdot (-4)=0,16.20 7) 4,4.1,89=9,9.0,84 8) -0,7cdot (-0,5)=3,5 9) -0,4cdot 1,5=-3.0,2 10) (-1)/(5)cdot 2=(-2)/(7)cdot 1(2)/(5) 11) 1(1)/(2):(2)/(3)=(1)/(4):(1)/(9) 12) 1(3)/(4):(1)/(2)=7:2

## Bài 1:<br /><br />1. **-0,8 : (-4) = 0,2** và **0,6 : 3 = 0,2**. Hai phép tính có cùng kết quả nên bằng nhau.<br />2. **$2\frac {1}{3}:3\frac {1}{4} = \frac{7}{3} : \frac{13}{4} = \frac{7}{3} \cdot \frac{4}{13} = \frac{28}{39}$** và **7 : 13 = $\frac{7}{13}$**. Hai phép tính có kết quả khác nhau nên không bằng nhau.<br /><br />## Bài 2:<br /><br />**1) 4.15 = 30.2**<br /><br />* $\frac{4}{30} = \frac{2}{15}$<br />* $\frac{4}{2} = \frac{30}{15}$<br />* $\frac{15}{30} = \frac{2}{4}$<br />* $\frac{15}{2} = \frac{30}{4}$<br /><br />**2) 5.20 = 2.50**<br /><br />* $\frac{5}{2} = \frac{50}{20}$<br />* $\frac{5}{50} = \frac{2}{20}$<br />* $\frac{20}{2} = \frac{50}{5}$<br />* $\frac{20}{50} = \frac{2}{5}$<br /><br />**3) 15.42 = 21.30**<br /><br />* $\frac{15}{21} = \frac{30}{42}$<br />* $\frac{15}{30} = \frac{21}{42}$<br />* $\frac{42}{21} = \frac{30}{15}$<br />* $\frac{42}{30} = \frac{21}{15}$<br /><br />**4) 0,36.4,25 = 0,9.1,7**<br /><br />* $\frac{0,36}{0,9} = \frac{1,7}{4,25}$<br />* $\frac{0,36}{1,7} = \frac{0,9}{4,25}$<br />* $\frac{4,25}{0,9} = \frac{1,7}{0,36}$<br />* $\frac{4,25}{1,7} = \frac{0,9}{0,36}$<br /><br />**5) -0,8.(-4) = 0,16.20**<br /><br />* $\frac{-0,8}{0,16} = \frac{20}{-4}$<br />* $\frac{-0,8}{20} = \frac{0,16}{-4}$<br />* $\frac{-4}{0,16} = \frac{20}{-0,8}$<br />* $\frac{-4}{20} = \frac{0,16}{-0,8}$<br /><br />**6) (-0,3):2,7 = (-1,7):15,3**<br /><br />* $\frac{-0,3}{-1,7} = \frac{2,7}{15,3}$<br />* $\frac{-0,3}{2,7} = \frac{-1,7}{15,3}$<br />* $\frac{15,3}{-1,7} = \frac{2,7}{-0,3}$<br />* $\frac{15,3}{2,7} = \frac{-1,7}{-0,3}$<br /><br />**7) 4,4.1,89 = 9,9.0,84**<br /><br />* $\frac{4,4}{9,9} = \frac{0,84}{1,89}$<br />* $\frac{4,4}{0,84} = \frac{9,9}{1,89}$<br />* $\frac{1,89}{9,9} = \frac{0,84}{4,4}$<br />* $\frac{1,89}{0,84} = \frac{9,9}{4,4}$<br /><br />**8) -0,7.(-0,5) = 3,5**<br /><br />* $\frac{-0,7}{3,5} = \frac{-0,5}{-0,7}$<br />* $\frac{-0,7}{-0,5} = \frac{3,5}{-0,7}$<br />* $\frac{3,5}{-0,7} = \frac{-0,5}{-0,7}$<br />* $\frac{3,5}{-0,5} = \frac{-0,7}{-0,7}$<br /><br />**9) -0,4.1,5 = -3.0,2**<br /><br />* $\frac{-0,4}{-3} = \frac{0,2}{1,5}$<br />* $\frac{-0,4}{0,2} = \frac{-3}{1,5}$<br />* $\frac{1,5}{-3} = \frac{0,2}{-0,4}$<br />* $\frac{1,5}{0,2} = \frac{-3}{-0,4}$<br /><br />**10) $\frac {-1}{5}\cdot 2=\frac {-2}{7}\cdot 1\frac {2}{5}$**<br /><br />* $\frac{-1/5}{-2/7} = \frac{1\frac{2}{5}}{2}$<br />* $\frac{-1/5}{1\frac{2}{5}} = \frac{-2/7}{2}$<br />* $\frac{2}{-2/7} = \frac{1\frac{2}{5}}{-1/5}$<br />* $\frac{2}{1\frac{2}{5}} = \frac{-2/7}{-1/5}$<br /><br />**11) $1\frac {1}{2}:\frac {2}{3}=\frac {1}{4}:\frac {1}{9}$**<br /><br />* $\frac{1\frac{1}{2}}{\frac{1}{4}} = \frac{\frac{2}{3}}{\frac{1}{9}}$<br />* $\frac{1\frac{1}{2}}{\frac{2}{3}} = \frac{\frac{1}{4}}{\frac{1}{9}}$<br />* $\frac{\frac{1}{4}}{\frac{1}{9}} = \frac{\frac{2}{3}}{1\frac{1}{2}}$<br />* $\frac{\frac{1}{4}}{\frac{2}{3}} = \frac{\frac{1}{9}}{1\frac{1}{2}}$<br /><br />**12) $1\frac {3}{4}:\frac {1}{2}=7:2$**<br /><br />* $\frac{1\frac{3}{4}}{7} = \frac{\frac{1}{2}}{2}$<br />* $\frac{1\frac{3}{4}}{\frac{1}{2}} = \frac{7}{2}$<br />* $\frac{2}{7} = \frac{\frac{1}{2}}{1\frac{3}{4}}$<br />* $\frac{2}{\frac{1}{2}} = \frac{7}{1\frac{3}{4}}$ <br />