Số?
a) \(\dfrac{2}{5}=\dfrac{2\times3}{5\times3}=\dfrac{?}{?}\) \(\dfrac{4}{7}=\dfrac{4\times2}{7\times2}=\dfrac{?}{?}\) \(\dfrac{13}{54}=\dfrac{13\times3}{54\times3}=\dfrac{?}{?}\)
b) \(\dfrac{8}{20}=\dfrac{8:4}{20:4}=\dfrac{?}{?}\) \(\dfrac{10}{16}=\dfrac{10:2}{16:2}=\dfrac{?}{?}\) \(\dfrac{25}{65}=\dfrac{25:5}{65:5}=\dfrac{?}{?}\)
a) \(\dfrac{2}{5}=\dfrac{2\times3}{5\times3}=\dfrac{6}{15}=\dfrac{2}{5}\)
\(\dfrac{4}{7}=\dfrac{4\times2}{7\times2}=\dfrac{8}{14}=\dfrac{4}{7}\)
\(\dfrac{13}{54}=\dfrac{13\times3}{54\times3}=\dfrac{39}{162}=\dfrac{13}{54}\)
b) \(\dfrac{8}{20}=\dfrac{8:4}{20:4}=\dfrac{2}{5}\)
\(\dfrac{10}{16}=\dfrac{10:2}{16:2}=\dfrac{5}{8}\)
\(\dfrac{25}{65}=\dfrac{25:5}{65:5}=\dfrac{5}{13}\)
(a x 3) : (b x 3) a : b 
(a : 2) : (b : 2)
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