28/25:7/15x5
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a.9/20-8/15x5/12
=9/20-2/9
=41/180
b.2/3:4/5:7/12
=5/6:7/12
=10/7
c.4/9+11/8-5/6
=131/72-5/6
=71/72
tk mk nhé bạn
\(\left(-\dfrac{7}{23}\right).\left(\dfrac{13}{28}\right)+\left(-\dfrac{7}{23}\right).\left(\dfrac{25}{28}\right)\)
\(=\left(-\dfrac{7}{23}\right).\left(\dfrac{13}{28}+\dfrac{25}{28}\right)\)
\(=\left(-\dfrac{7}{23}\right).\left(\dfrac{38}{28}\right)\)
\(=\left(-\dfrac{7}{23}\right).\left(\dfrac{19}{14}\right)\)
\(=-\dfrac{19}{46}\)
\(\left(-\dfrac{7}{23}\right)\cdot\left(\dfrac{13}{28}\right)+\left(-\dfrac{7}{13}\right)\cdot\left(\dfrac{25}{28}\right)\)
\(=\left(-\dfrac{7}{23}\right)\cdot\left(\dfrac{13}{28}+\dfrac{25}{28}\right)\)
\(=\left(-\dfrac{7}{13}\right)\cdot\dfrac{38}{28}\)
\(=\left(-\dfrac{7}{13}\right)\cdot\dfrac{19}{14}\)
\(=-\dfrac{19}{26}\)
Ta có :
\(\dfrac{4}{5}=\dfrac{140}{175};\dfrac{28}{5}=\dfrac{196}{175};\dfrac{28}{7}=\dfrac{700}{175};\dfrac{25}{25}=\dfrac{175}{175};\dfrac{2}{5}=\dfrac{70}{175}\\ \dfrac{70}{175}< \dfrac{140}{175}< \dfrac{175}{175}< \dfrac{700}{175}< \dfrac{980}{175}\\ \Rightarrow\dfrac{2}{5}< \dfrac{4}{5}< \dfrac{25}{25}< \dfrac{28}{7}< \dfrac{28}{5}\)
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