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a: 4/9+3/7=28/63+27/63=55/63
3/4+7/24=18/24+7/24=25/24
1/3+2/9+4/27=9/27+6/27+4/27=19/27
b: 5/6-3/8=20/24-9/24=11/24
7/15-11/30=14/30-11/30=3/30=1/10
2/3+1/6-7/12
=8/12+2/12-7/12
=3/12=1/4
c: 18/25*15/6=15/25*18/6=3*3/5=9/5
30/49:6/7=30/49*7/6=210/294=5/7
1/2*3/4:6/5=3/8*5/6=15/48=5/16
d: 8*3/5:12/5=24/5*5/12=2
4:9/5:10/3=4*5/9*3/10=2/3
11/9-5/6:15
=11/9-5/6.1/15
=11/9-1/18
=7/6
3/16+(-7/30).15/28
=3/16+(-1/8)
=3/16+(-2/16)
=1/16
\(\dfrac{11}{9}-\dfrac{5}{6}:15=\dfrac{11}{9}-\dfrac{5}{6}\times\dfrac{1}{15}=\dfrac{11}{9}-\dfrac{5}{90}=\dfrac{110}{90}-\dfrac{5}{90}=\dfrac{105}{90}=\dfrac{7}{6}\)
\(\dfrac{3}{16}+\dfrac{-7}{30}\times\dfrac{15}{28}=\dfrac{3}{16}+\left(-\dfrac{1}{8}\right)=\dfrac{3}{16}-\dfrac{1}{8}=\dfrac{3}{16}-\dfrac{2}{16}=\dfrac{1}{16}\)
1 kg 
2 m
a)
\(\dfrac{5}{8}\left(kg\right)< \dfrac{6}{8}\left(kg\right)\)
Do 13 > 12 nên \(\dfrac{13}{12}>1\)
hay: \(\dfrac{13}{12}\left(kg\right)>1\left(kg\right)\)
b)
\(\dfrac{11}{12}\left(l\right)>\dfrac{11}{14}\left(l\right)\)
Có:
\(\dfrac{5}{3}=\dfrac{5\times3}{3\times3}=\dfrac{15}{9}\)
nên: \(\dfrac{5}{3}\left(l\right)=\dfrac{15}{9}\left(l\right)\)
c)
\(\dfrac{5}{6}=\dfrac{5\times3}{6\times3}=\dfrac{15}{18n}\)
nên \(\dfrac{5}{6}\left(m\right)< \dfrac{17}{8}\left(m\right)\)
Có: \(2=\dfrac{2\times7}{7}=\dfrac{14}{7}\)
nên: \(\dfrac{16}{7}\left(m\right)>2\left(m\right)\)
\(=\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\cdot\dfrac{10-6-3-1}{30}=0\)
\(\left(\dfrac{1}{3}-\dfrac{1}{5}-\dfrac{1}{10}-\dfrac{1}{30}\right)\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=\left(\dfrac{10}{30}-\dfrac{6}{30}-\dfrac{3}{30}-\dfrac{1}{30}\right)\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=0\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=0\)
Chọn D
Oki, thank you bạn nhiều