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a, 2/5 + 1/6 + 3/5
= ( 2/5 + 3/5 ) + 1/6
= 5/5 + 1/6
= 1 + 1/6
= 6/6 + 1/6
= 7/6
b, 9/13 + 4/13 + 2/3
= 13/13 + 2/3
= 1 + 2/3
= 3/3 + 2/3
= 5/3
2/5+1/6+3/5
=(2/5+3/5)+1/6
=5/5+1/6
=1+1/6
=7/6
9/13+4/13+2/3
=(9/13+4/13)+2/3
=13/13+2/3
=1+2/3
=5/3
k mk nha các bạn, nhớ kb mk đó
a. \(\dfrac{17}{13}-\dfrac{14}{23}+\dfrac{9}{13}-\dfrac{9}{23}=\left(\dfrac{17}{13}+\dfrac{9}{13}\right)-\left(\dfrac{14}{23}+\dfrac{9}{23}\right)=\dfrac{26}{13}-\dfrac{23}{23}=2-1=1\)
b.\(\dfrac{49}{5}-\dfrac{1}{2}-\dfrac{1}{4}-\dfrac{1}{32}-\dfrac{1}{16}-\dfrac{1}{32}=\dfrac{49}{5}-\left(1-\dfrac{1}{32}\right)=\dfrac{44}{5}+\dfrac{1}{32}=\dfrac{1413}{160}\)
a: =20/90+15/90+54/90=89/90
b: =(9/13+4/13)+2/3=1+2/3=5/3
`4/6+7/13+17/9+19/13+1/9+14/6`
`=(4/6+14/6)+(7/13+19/13)+(17/9+1/9)`
`=18/6+26/13+18/9`
`=3+2+2`
`=7`
\(\frac{7}{4}\times\frac{15}{7}+\frac{13}{7}\times\frac{9}{4}-\frac{2}{7}\)
\(=\left(\frac{7}{4}+\frac{9}{4}\right)\times\left(\frac{15}{7}+\frac{13}{7}\right)-\frac{2}{7}\)
\(=4\times4-\frac{2}{7}\)
\(=16-\frac{2}{7}\)
\(=\frac{112}{7}-\frac{2}{7}\)
\(=\frac{110}{7}\)
\(\dfrac{4}{13}+\dfrac{1}{2}+\dfrac{9}{13}=\left(\dfrac{4}{13}+\dfrac{9}{13}\right)+\dfrac{1}{2}=1+\dfrac{1}{2}=\dfrac{3}{2}\)