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a) \(\dfrac{3}{5}+\dfrac{7}{25}=\dfrac{15}{25}+\dfrac{7}{25}=\dfrac{15+7}{25}=\dfrac{22}{25}\)
b) \(\dfrac{8}{11}-\dfrac{19}{33}=\dfrac{24}{33}-\dfrac{19}{33}=\dfrac{24-19}{33}=\dfrac{5}{33}\)
c) \(\dfrac{16}{21}\times\dfrac{3}{5}=\dfrac{16\times3}{21\times5}=\dfrac{48}{105}=\dfrac{16}{35}\)
d) \(\dfrac{14}{41}\div\dfrac{7}{9}=\dfrac{14}{41}\times\dfrac{9}{7}=\dfrac{14\times9}{41\times7}=\dfrac{126}{287}=\dfrac{18}{41}\)
a)
\(\dfrac{5}{6}< \dfrac{7}{6}\)
\(2=\dfrac{6}{3}\)
\(\dfrac{3}{7}>\dfrac{4}{14}\) (vì \(\dfrac{4}{14}=\dfrac{2}{7}\))
\(\dfrac{12}{20}< \dfrac{4}{5}\) (vì \(\dfrac{12}{20}=\dfrac{3}{5}\))
b)
\(\dfrac{1}{13}=\dfrac{3}{39};\dfrac{25}{13}=\dfrac{75}{39}\)
\(\dfrac{75}{39}>\dfrac{4}{39}>\dfrac{3}{39}\rightarrow\dfrac{75}{39},\dfrac{4}{39},\dfrac{3}{39}\)
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\(\dfrac{2}{8}=\dfrac{4}{16};\dfrac{7}{4}=\dfrac{28}{16}\)
\(\dfrac{28}{16}>\dfrac{9}{16}>\dfrac{4}{16}\rightarrow\dfrac{28}{16},\dfrac{9}{16},\dfrac{4}{16}\)
a) \(\dfrac{3}{5}+\dfrac{11}{20}=\dfrac{12}{20}+\dfrac{11}{20}=\dfrac{23}{20}\)
b) \(\dfrac{5}{8}-\dfrac{4}{9}=\dfrac{45}{72}-\dfrac{32}{72}=\dfrac{13}{72}\)
c) \(\dfrac{9}{16}\times\dfrac{4}{3}=\dfrac{3}{4}\)
d) \(\dfrac{4}{7}:\dfrac{8}{11}=\dfrac{4}{7}\times\dfrac{11}{8}=\dfrac{11}{14}\)
e) \(\dfrac{3}{5}+\dfrac{4}{5}:\dfrac{2}{5}=\dfrac{3}{5}+\dfrac{4}{5}\times\dfrac{5}{2}=\dfrac{3}{5}+2=\dfrac{3}{5}+\dfrac{10}{5}=\dfrac{13}{5}\)
Lời giải:
$\frac{25}{16}-\frac{7}{20}=\frac{25\times 5}{16\times 5}-\frac{7\times 4}{20\times 4}$
$=\frac{125}{80}-\frac{28}{80}=\frac{97}{80}$