Đáp án:
$3a)
\dfrac{a}{b}=\dfrac{2}{3}\\
b)\dfrac{a}{b}=\dfrac{4}{3}\\
c)
\dfrac{a}{b}=60\\
d) \dfrac{a}{b}=\dfrac{9}{5}\\
e)\dfrac{a}{b}=0,03$
Giải thích các bước giải:
$3a)
\dfrac{a}{b}=\dfrac{12}{18}=\dfrac{12:6}{18:6}=\dfrac{2}{3}\\
b)\dfrac{a}{b}=\dfrac{1,25}{\dfrac{15}{16}}=\dfrac{\dfrac{125}{100}}{\dfrac{15}{16}}=\dfrac{\dfrac{125:25}{100:25}}{\dfrac{15}{16}}\\
=\dfrac{\dfrac{5}{4}}{\dfrac{15}{16}}=\dfrac{5.16}{4.15}=\dfrac{5.4^2}{4.5.3}=\dfrac{4}{3}\\
c)a=0,75dm^2=0,75.100cm^2=75cm^2\\
b=1,25cm^2\\
\dfrac{a}{b}=\dfrac{75}{1,25}=\dfrac{75}{\dfrac{125}{100}}=\dfrac{75}{\dfrac{5}{4}}=\dfrac{75.4}{5}=\dfrac{15.5.4}{5}=60\\
d)
a=\dfrac{3}{5}h\\
b=20p=\dfrac{20}{60}h=\dfrac{1}{3}h\\
\dfrac{a}{b}=\dfrac{\dfrac{3}{5}}{\dfrac{1}{3}}=\dfrac{3.3}{5}=\dfrac{9}{5}\\
e)a=\dfrac{3}{5}dm^3\\
b=20 (l)=20dm^3\\
\dfrac{a}{b}=\dfrac{\dfrac{3}{5}}{20}=\dfrac{3}{5.20}=\dfrac{3}{100}=0,03$
