21 phần ...... nhân 3=2một phần hai
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, 3/22 x 3/11 x 22
Cách 1
3/22 x 3/11 x 22 = 9/242 x 22
= 198/242
= 9/11
Cách 2
3/22 x 3/11 x 22 = 3 x 3 x 22/22 x 11 x 1
= 9/11
b,( 1/2 + 1/3) x 2/5
Cách 1
( 1/2 + 1/3 ) x 2/5 = 5/6 x 2/5
= 10/30
= 1/3
Cách 2
( 1/2 +1/3) x 2/5 = 1/2 x 2/5 + 1/3 x 2/5
= 2/10 + 2/15
= 1/5 + 2/15
= 3/15 + 2/15
= 5/15
= 1/3
c, 3/5 x 17/21 + 17/21 x 2/5
Cách 1
3/5 x 17/21 + 17/21 x 2/5 = 51/105 + 34/105
= 85/105
= 17/21
Cách 2
3/5 x 17/21 + 17/21 x 2/5 = 17/21 x (3/5 +2/5)
= 17/21 x 5/5
= 17/21 x 1
= 17/21
HỌC TỐT ( k mk nhé)
![](https://rs.olm.vn/images/avt/0.png?1311)
dễ, nhưng phai giai dc câu nay 60% nhan x cong 2 phan 3 = 1 phan 3 nhan 6va 1 phan 3
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{3}\times x+\frac{3}{4}\times x-75\%=\frac{-21}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{-7}{8}:\dfrac{21}{16}-\dfrac{5}{3}.\left(\dfrac{1}{5}-\dfrac{7}{10}\right)\)
\(=\dfrac{-7}{8}.\dfrac{16}{21}-\dfrac{5}{3}.\left(\dfrac{-1}{2}\right)\)
\(=\dfrac{-2}{3}+\dfrac{5}{6}=\dfrac{1}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{5}{5}x\)\(\frac{17}{21}+\frac{17}{21}x\)\(\frac{2}{5}\)
=(\(\frac{5}{5}+\frac{2}{5}\)) x\(\frac{17}{21}\)
=\(\frac{7}{5}x\)\(\frac{17}{21}\)
\(\frac{119}{105}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a 25 phần 41
b 9
c 1 phần 12
d 12
e 14 phần 15
f 24 phần 7
\(\frac{21}{...\times3}=2\frac{1}{2}\)
\(\frac{21}{...\times3}=\frac{5}{2}\)
\(\frac{21\times5}{...\times3\times5}=\frac{5\times21}{2\times21}\) (qui đồng tử số)
=> ... x 3 x 5 = 2 x 21 = 42
=> ... = 42/15