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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
Ta có :
\(\dfrac{4}{5}=\dfrac{140}{175};\dfrac{28}{5}=\dfrac{196}{175};\dfrac{28}{7}=\dfrac{700}{175};\dfrac{25}{25}=\dfrac{175}{175};\dfrac{2}{5}=\dfrac{70}{175}\\ \dfrac{70}{175}< \dfrac{140}{175}< \dfrac{175}{175}< \dfrac{700}{175}< \dfrac{980}{175}\\ \Rightarrow\dfrac{2}{5}< \dfrac{4}{5}< \dfrac{25}{25}< \dfrac{28}{7}< \dfrac{28}{5}\)
\(=\dfrac{1}{3\times8}=\dfrac{1}{24}\\ =\dfrac{6}{11}\times\dfrac{11}{3}=2\)
\(\frac{9}{20}-\frac{8}{15}\cdot\frac{5}{12}=\frac{9}{20}-\frac{8\cdot5}{15\cdot12}=\frac{9}{20}-\frac{2\cdot1}{3\cdot3}=\frac{9}{20}-\frac{2}{9}=\frac{81}{180}-\frac{40}{180}=\frac{41}{180}\)
\(\frac{9}{20}-\frac{8}{15}\times\frac{5}{12}=\frac{9}{20}-\frac{8\times5}{15\times12}=\frac{9}{20}-\frac{2\times4\times5}{3\times5\times3\times4}=\frac{9}{20}-\frac{2}{9}=\frac{81}{180}-\frac{40}{180}=\frac{41}{180}\)
a) 2/5 + 1/2 + 7/10
= 4/10 + 5/10 + 7/10
= 9/10 + 7/10
= 16/10 = 8/5
b) 4/9 + 11/8 - 5/6
= 32/72 + 99/72 - 60/72
= 191/72
c) 9/20 - 8/15 x 5/12
= 9/20 - 2/9
= 41/180
d) 2/3 : 4/5 : 7/12
= 5/6 : 7/12
= 10/7
12
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