`5`

`a, -7/21 +(1+1/3)`

`=-7/21 + ( 3/3 + 1/3)`

`=-7/21+ 4/3`

`=-7/21+ 28/21`

`= 21/21`

`=1`

`b, 2/15 + ( 5/9 + (-6)/9)`

`= 2/15 + (-1/9)`

`= 1/45`

`c, (9-1/5+3/12) +(-3/4)`

`= ( 45/5-1/5 + 3/12)+(-3/4)`

`= ( 44/5 + 3/12)+(-3/4)`

`= 9,05 +(-0,75)`

`=8,3`

`6`

`x+7/8 =13/12`

`=>x= 13/12 -7/8`

`=>x=5/24`

`-------`

`-(-6)/12 -x=9/48`

`=> 6/12 -x=9/48`

`=>x= 6/12-9/48`

`=>x=5/16`

`---------`

`x+4/6 =5/25 -(-7)/15`

`=>x+4/6 =1/5 + 7/15`

`=> x+ 4/6=10/15`

`=>x=10/15 -4/6`

`=>x=0`

`----------`

`x+4/5 = 6/20 -(-7)/3`

`=>x+4/5 = 6/20 +7/3`

`=>x+4/5 = 79/30`

`=>x=79/30 -4/5`

`=>x= 79/30-24/30`

`=>x= 55/30`

`=>x= 11/6`

\(5)\)

\(A=\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)\)

\(A=\dfrac{-7}{21}+\dfrac{4}{3}\)

\(A=\dfrac{-7}{21}+\dfrac{28}{21}\)

\(A=1\)

\(--------------\)

\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)\)

\(B=\dfrac{2}{15}+\dfrac{-1}{9}\)

\(B=\dfrac{18}{135}+\dfrac{-15}{135}\)

\(B=\dfrac{1}{45}\)

\(------------\)

\(C=9-\dfrac{1}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)

\(C=\dfrac{44}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)

\(C=\dfrac{528}{60}+\dfrac{15}{60}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-15}{20}\)

\(C=\dfrac{83}{10}\)

\(6)\)

\(a)\) \(x+\dfrac{7}{8}=\dfrac{13}{12}\)

\(x=\dfrac{13}{12}-\dfrac{7}{8}\)

\(x=\dfrac{104}{96}-\dfrac{84}{96}\)

\(x=\dfrac{5}{24}\)

\(b)\) \(\dfrac{-6}{12}-x=\dfrac{9}{48}\)

\(\dfrac{-1}{2}-x=\dfrac{3}{16}\)

\(x=\dfrac{-1}{2}-\dfrac{3}{16}\)

\(x=\dfrac{-8}{16}-\dfrac{3}{16}\)

\(x=\dfrac{-11}{16}\)

\(c)\) \(x+\dfrac{4}{6}=\dfrac{5}{25}-\left(-\dfrac{7}{15}\right)\)

\(x+\dfrac{4}{6}=\dfrac{5}{25}+\dfrac{7}{15}\)

\(x+\dfrac{4}{6}=\dfrac{75}{375}+\dfrac{105}{375}\)

\(x+\dfrac{4}{6}=\dfrac{12}{25}\)

\(x=\dfrac{12}{25}-\dfrac{4}{6}\)

\(x=\dfrac{72}{150}-\dfrac{100}{150}\)

\(x=\dfrac{-14}{75}\)

\(d)\) \(x+\dfrac{4}{5}=\dfrac{6}{20}-\left(-\dfrac{7}{3}\right)\)

\(x+\dfrac{4}{5}=\dfrac{6}{20}+\dfrac{7}{3}\)

\(x+\dfrac{4}{5}=\dfrac{18}{60}+\dfrac{140}{60}\)

\(x+\dfrac{4}{5}=\dfrac{79}{30}\)

\(x=\dfrac{79}{30}-\dfrac{4}{5}\)

\(x=\dfrac{79}{30}-\dfrac{24}{30}\)

\(x=\dfrac{11}{6}\)

a) 9 x 5 + 9 = 45 + 9     b) 9 x 2 + 9 = 18 + 9

   = 54     = 27

c) 9 x 7 + 9 = 63 + 9     d) 9 x 6 + 9 = 54 + 9

   = 70     = 63

a) 9 x 4 + 9 = 36 + 9 = 45

b) 9 x 6 + 9 = 54 + 9 = 63

c) 9 x 5 + 9 = 45 + 9 = 54

d) 9 x 7 + 9 = 63 + 9 = 72

`a)1/7xx2/7+1/7xx5/7+6/7`

`=1/7xx(2/7+5/7)+6/7`

`=1/7xx1+6/7`

`=1/7+6/7=1`

`b)6/11xx4/9+6/11xx7/9-6/11xx2/9`

`=6/11xx(4/9+7/9-2/9)`

`=6/11xx9/9`

`=6/11`

Sorry nãy ghi thiếu.

`c)4/25xx5/8xx25/4xx24`

`=(4xx5xx25xx24)/(25xx8xx4)`

`=(4xx5xx24)/(4xx8)`

`=(5xx24)/8`

`=5xx3=15`

\(a,x=\dfrac{4}{5}\times\dfrac{1}{3}=\dfrac{4}{15}\)

\(b,x=\dfrac{7}{9}\times\dfrac{3}{5}=\dfrac{7}{15}\)

\(c,x=\dfrac{7}{6}\times\dfrac{4}{3}=\dfrac{14}{9}\\ d,x=\dfrac{9}{7}\times\dfrac{8}{4}=\dfrac{18}{7}\)

X=4/15

X=7/15

X=14/9

X=18/7

a, x + \(\dfrac{1}{5}\) = \(\dfrac{5}{6}\)

x = \(\dfrac{5}{6}\) - \(\dfrac{1}{5}\)

x = \(\dfrac{19}{30}\)

b, x - \(\dfrac{3}{5}=\dfrac{6}{7}\)

x = \(\dfrac{6}{7}+\dfrac{3}{5}\)

x = \(1\dfrac{16}{35}\)

c, - x - \(\dfrac{7}{5}=\dfrac{-8}{9}\)

- x = \(\dfrac{-8}{9}+\dfrac{7}{5}\)

x = \(\dfrac{23}{45}\)

d, \(\dfrac{3}{8}-x=\dfrac{2}{3}\)

\(x=\dfrac{3}{8}-\dfrac{2}{3}\)

\(x=\dfrac{-7}{24}\)

e, \(|x-\dfrac{8}{9}|=\dfrac{1}{3}\)

\(x=\dfrac{1}{3}+\dfrac{8}{9}\)

\(x=\dfrac{-11}{9}\)

Hiệu giữa SBT mới và cũ là:

353 – 23 = 330

Hiệu số phần bằng nhau là:

3-1 = 2 phần

Số bị trừ cũ là: 330 : 2 = 165

Số trừ cũ là : 165- 23 = 142

 a)\(\left(\dfrac{5}{6}+\dfrac{3}{8}\right)\times\dfrac{2}{7}\)

\(=\dfrac{29}{24}\times\dfrac{2}{7}\)

\(=\) \(\dfrac{29}{84}\)

b) \(\dfrac{6}{7}\times\dfrac{2}{3}\div\dfrac{5}{7}\)

= \(\dfrac{4}{7}\div\) \(\dfrac{5}{7}\)

= \(\dfrac{4}{5}\)

c) \(\dfrac{8}{9}+\dfrac{3}{4}\times\dfrac{4}{9}\)

= \(\dfrac{8}{9}+\dfrac{1}{3}\)

= \(\dfrac{5}{9}\)

Cô tích xanh cho lisa blackpink vì câu a, b đúng. Còn câu c thì em làm như sau:

c, \(\dfrac{8}{9}\) + \(\dfrac{3}{4}\) \(\times\) \(\dfrac{4}{9}\) 

  = \(\dfrac{8}{9}\) + \(\dfrac{1}{3}\)

  =  \(\dfrac{8}{9}\) + \(\dfrac{3}{9}\)

  =    \(\dfrac{11}{9}\)

a,\(\frac{6\times7\times8}{8\times9\times10}=\frac{6\times7}{9\times10}=\frac{7}{15}\)

\(\frac{7}{8}.\frac{9}{11}.\frac{8}{3}:\frac{2}{9}\)

\(=\frac{7.9.8.9}{8.11.3.2}\)

\(=\frac{189}{11}\)

Dấu \(\left(.\right)\)là dấu nhân nhé