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a) 2/5 x 1/4 + 3/4 x 2/5
= 2/5 x (1/4 + 3/4)
= 2/5 x 1
= 2/5
b) 6/11 : 2/3 + 5/11 : 2/3
= (6/11 + 5/11) : 2/3
= 1 : 2/3
= 3/2
1.
\(a,\dfrac{3}{4}+\dfrac{5}{2}=\dfrac{3}{4}+\dfrac{10}{4}=\dfrac{13}{4}\)
\(b,3+\dfrac{6}{11}+\dfrac{33}{11}+\dfrac{6}{11}=\dfrac{39}{11}\)
\(c,2-\dfrac{5}{7}=\dfrac{14}{7}-\dfrac{5}{7}=\dfrac{9}{7}\)
\(\dfrac{11}{3}-2=\dfrac{11}{3}-\dfrac{6}{3}=\dfrac{5}{3}\)
2.
\(a,\dfrac{13}{19}+\dfrac{18}{19}+\dfrac{17}{19}=\dfrac{13}{19}+\dfrac{17}{19}+\dfrac{18}{19}=\dfrac{30}{19}+\dfrac{18}{19}=\dfrac{48}{19}\)
\(b,\dfrac{3}{5}+\dfrac{3}{16}+13+16=\dfrac{63}{80}+29=\dfrac{2383}{80}\)
3.
Nửa chu vi :
\(4:2=2\left(m\right)\)
Chiều rộng :
\(2-\dfrac{5}{6}=\dfrac{7}{6}\left(m\right)\)
a,Cách 1: (6/11 + 5/11 ) x 3/7 Cách 2 :(6/11 + 5/11) x 3/7
= 1 x 3/7 =6/11 x 3/7 + 5/11 x 3/7
= 3/7 = 18/77 + 15/77
= 3/7
b, Cách 1:3/5 x 7/9 - 3/5 x 2/9 Cách 2 :3/5 x 7/9 - 3/5 x 2/9
= 7/15 - 2/15 = 3/5 x (7/9 - 2/9 )
= 1/3 = 3/5 x 5/9
= 1/3
c, Cách 1:(6/7 - 4/7) : 2/5 Cách 2: ( 6/7- 4/7 ) : 2/5
= 2/7 : 2/5 = 6/7 : 2/5 - 4/7 : 2/5
= 5/7 = 15/7 - 10/7
= 5/7
d,Cách 1:8/15 : 2/11 + 7/15 : 2/11 Cách 2:8/15 : 2/11 +7/15 : 2/11
= 88/30 + 77/30 =(8/15+7/15) :2/11
= 11/2 = 1 : 2/11
= 11/2
Bài 2 cậu tự làm nhé !
`1/3 + 1/5 -1/4`
`= 5/15 + 3/15 -1/4`
`= 8/15 -1/4`
`= 17/60`
__
`7/8 -(1/4 + 2/5)`
`= 7/8-1/4 - 2/5`
`= 7/8 - 2/8 -2/5`
`= 5/8 -2/5`
`= 9/40`
__
`5/11-(3/5 -6/11)`
`= 5/11 -3/5 +6/11`
`= (5/11 + 6/11)-3/5`
`= 1 -3/5`
`= 5/5-3/5`
`=2/5`
__
`5/7 - ( 19/35 - 6/15)`
`= 5/7 - 19/35 + 6/15`
`= 25/35 -19/35 + 6/15`
`=6/35 +6/15`
`=4/7`
1/3 + 1/5 - 1/4 = 17/60
7/8 - (1/4 + 2/5) = 9/40
5/11 - (3/5 - 6/11) = 2/5
3:
3/5:x=3
=>x=3/5:3=1/5
4:
a:
=1/5+4/5+4/11+7/11=1+1=2
b: =5/6+5/9-1/4
=30/36+20/36-9/36
=41/36
5: Tổng hai số là 100
Số bé là 100*2/5=40
Số lớn là 100-40=60
\(\dfrac{11}{5}-\dfrac{3}{4}=\dfrac{44}{20}-\dfrac{15}{20}=\dfrac{29}{20}\)
\(\dfrac{11}{5}-\dfrac{3}{4}=\dfrac{29}{20}\)