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A)6 và 4/5-(1 và 2/3+3 và 4/5)
=6+4/5-1-2/3-3-4/5
=(6-1-3)+(4/5-4/5)-2/3
=2-2/3=1 và 1/3
B)[(19+5/8/7/12)-(13+1/4/7/12)]X4/5
=[(19-13)+(5/8/7/12-1/4/7/12)]X4/5
=[6+3/8/7/12]X4/5
=[6+9/14]X4/5
=93/14 X4/5=186/35
nhớ
\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)=\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)
\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}=2+\frac{8}{13}\)
\(=\frac{26}{13}+\frac{8}{13}=\frac{34}{13}\)
\(a.32,5-3\cdot0,87=32,5-2,61=29,89\)
\(8,5\cdot\left(1\dfrac{1}{2}+\dfrac{4}{4}\right):5=8,5\cdot\left(\dfrac{3}{2}+\dfrac{4}{4}\right):5\\ =8,5\cdot\left(\dfrac{6}{4}+\dfrac{4}{4}\right):5\\ =8,5\cdot\dfrac{10}{4}:5\\ =\dfrac{85}{4}:5\\ =\dfrac{17}{4}\)
\(b.30,96-6,45+14,4:3=30,96-6,45+4,8\\ =29,31\)
\(\dfrac{2}{5}\cdot\left(\dfrac{4}{5}-\dfrac{1}{2}\right)=\dfrac{2}{5}\cdot\left(\dfrac{8}{10}-\dfrac{5}{10}\right)\\ =\dfrac{2}{5}\cdot\dfrac{3}{10}=\dfrac{3}{25}\)
bài 2
\(a.2,5\cdot12,5\cdot8\cdot0,4=\left(2,5\cdot0,4\right)\left(12,5\cdot8\right)\\ =1\cdot100=100\)
b,\(\dfrac{12}{15}\cdot\dfrac{5}{6}\cdot\dfrac{3}{20}\cdot\dfrac{32}{5}=\dfrac{12\cdot5\cdot3\cdot32}{15\cdot6\cdot20\cdot5}\\ =\dfrac{3\cdot4\cdot5\cdot3\cdot4\cdot8}{3\cdot5\cdot2\cdot3\cdot5\cdot4\cdot5}=\dfrac{16}{25}\)
Bài 1:
a) \(32.5-3\cdot0.87=32.5-2.61=29.89\)
\(8.5\cdot\left(1\dfrac{1}{2}+\dfrac{4}{4}\right):5=8.5\cdot\dfrac{5}{2}:5=\dfrac{17}{2}\cdot\dfrac{5}{2}:5=\dfrac{85}{4}\cdot\dfrac{1}{5}=\dfrac{17}{4}\)
1/10+2/20+3/30+4/40+5/50+6/60+7/70+8/80+9/90
=1/10+1/10+1/10+1/10+1/10+1/10+1/10+1/10+1/10
=1/10 x 9 = 9/10
=7/70+7/70+7/70+7/70+7/70+7/70+7/70+7/70+7/70
=7/70*9/9
=63/630=1/10
\(\frac{5}{12}\times\frac{2}{3}+\frac{2}{3}\times\frac{7}{12}+\frac{1}{3}\)
\(=\frac{2}{3}\times\left(\frac{5}{12}+\frac{7}{12}\right)+\frac{1}{3}\)
\(=\frac{2}{3}\times1+\frac{1}{3}\)
\(=\frac{2}{3}+\frac{1}{3}\)
\(=1\)
\(\frac{5}{12}\times\frac{2}{3}+\frac{2}{3}\times\frac{7}{12}+\frac{1}{3}=\frac{2}{3}\times\left(\frac{5}{12}+\frac{7}{12}\right)+\frac{1}{3}\)
\(=\frac{2}{3}\times\frac{12}{12}+\frac{1}{3}=\frac{2}{3}\times1+\frac{1}{3}=\frac{2}{3}+\frac{1}{3}=\frac{3}{3}=1\)
Ta có : 1/10+2/20+3/30+4/40+5/50+6/60+7/70+8/80+9/90
= 1/10+1/10+1/10+1/10+1/10+1/10+1/10+1/10+1/10
= 1/10 . 9
= 9/10
Vậy.......
Tk và kb với mik nha !!!
7/9 + 4/5 + 2/9 + 1/5
= ( 7/9 + 2/9 ) + ( 4/5 + 1/5 )
= 1 + 1
= 2
~ Hok T ~
\(\frac{2}{3}\cdot\frac{4}{7}+\frac{2}{3}\cdot\frac{3}{7}\)
=\(\frac{2}{3}\left(\frac{4}{7}+\frac{3}{7}\right)\)
= \(\frac{2}{3}\cdot1\)
= \(\frac{2}{3}\)
`a, 3/5 \times 8/27 \times 5/3`
`= (3/5 \times 5/3)\times 8/27`
`= 1 \times8/27`
`= 8/27`
`b, 7/19 \times 1/3 + 7/19 \times 2/3`
`= 7/19 \times (1/3+2/3)`
`= 7/19 \times1`
`=7/19`
a)3/5 x 8/27 x 5/3
=( 3/5 x 5/3)x8/27
=1x8/27
=8/27
b)7/19 x 1/3 + 7/19 x 2/3
=(7/19 x 1/3) + (7/19 x 2/3)
=7/57 + 14/57
=7/19