Bài 3:
a) $\frac{36}{-48}$=$\frac{36:12}{-48:12}$ =$\frac{3}{-4}$
b) $\frac{-15}{50}$=$\frac{-15:5}{50:5}$=$\frac{-3}{10}$
c) $\frac{-18}{-81}$= $\frac{-18:(-9)}{-81:(-9)}$=$\frac{2}{9}$
d) $\frac{145}{215}$ =$\frac{145:5}{215:5}$ = $\frac{29}{43}$
Bài 4:
a) $\frac{-2.7}{7.5}$ = $\frac{-2}{5}$
b) $\frac{-21.(-5)}{15.(-7)}$= $\frac{3. (-7).(-1).5}{3.5.(-7)}$ = -1
c) $\frac{72.75}{125.108}$ = $\frac{36.2.25.3}{25.5.36.3}$ = $\frac{2}{5}$
d) $\frac{32.9.11}{12.24.22}$ = $\frac{4.8.3.3.11}{4.3.3.8.2.11}$ = $\frac{1}{2}$
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