13 – 6 + 8 = 7 + 8 = 15

7 + 5 – 9 = 12 – 9 = 3

17 – 8 + 6 = 9 + 6 = 15

7 + 9 – 12 = 16 – 12 = 4

14 + 6 – 17 = 20 – 17 = 3

51 + 18 – 40 = 69 – 40 = 29

43 + 7 – 21 = 50 – 21 = 29

6 + 4 – 8 = 10 – 8 = 2

12 – 3 + 8  = 9 + 8 = 17

\(a,\dfrac{1}{7}+\dfrac{1}{3}=\dfrac{3}{21}+\dfrac{7}{21}=\dfrac{10}{21}\\ b,\dfrac{-2}{3}+\dfrac{-5}{7}=\dfrac{-14+\left(-15\right)}{21}=\dfrac{-29}{21}\\ c,\dfrac{1}{2}-\dfrac{-1}{2}-\dfrac{1}{3}=\dfrac{3+3-2}{6}=\dfrac{4}{6}=\dfrac{2}{3}\)

\(a.\dfrac{4}{28}+\dfrac{12}{36}=\dfrac{1}{7}+\dfrac{1}{3}=\dfrac{3}{21}+\dfrac{7}{21}=\dfrac{10}{21}\\ b.\dfrac{-12}{18}+\dfrac{-15}{21}=\dfrac{-2}{3}+\dfrac{-5}{7}=\dfrac{-14}{21}+\dfrac{-15}{21}=\dfrac{-29}{21}\\ c.\dfrac{14}{28}+\dfrac{16}{32}-\dfrac{17}{51}=\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{17}{51}=1-\dfrac{17}{51}=\dfrac{2}{3}\)

\(\dfrac{4}{28}+\dfrac{12}{36}=\dfrac{144}{1008}+\dfrac{336}{1008}=\\ \dfrac{480}{1008}=\dfrac{10}{21}\)

Câu b và c em làm tương tự.

a) 9/22 x 33/18 =3/4

b) 12/35 : 36/25 = 5/21

c) 19/17 : 76/51 =3/4

a) \(\frac{9}{22}\times\frac{33}{18}\)

\(=\frac{9}{22}\times\frac{11}{6}\)

\(=\frac{9\times11}{22\times6}=\frac{3}{4}\)

b) \(\frac{12}{35}:\frac{36}{25}=\frac{12}{35}\times\frac{25}{36}\)

                     \(=\frac{5}{21}\)

c) \(\frac{19}{17}:\frac{76}{51}=\frac{19}{17}\times\frac{51}{76}\)

                      \(=\frac{3}{4}\)

\(a,\frac{9}{22}x\frac{33}{18}\)

\(=\frac{3.3.11.3}{11.2.3.3.2}\)

\(=\frac{3}{2.2}\)

\(=\frac{3}{4}\)

\(b,\frac{12}{35}:\frac{36}{25}\)

\(=\frac{12}{35}.\frac{25}{36}\)

\(=\frac{12.25}{35.36}\)

\(=\frac{12.5.5}{5.7.12.3}\)

\(=\frac{5}{7.3}\)

\(=\frac{5}{21}\)

\(c,\frac{19}{17}:\frac{76}{51}\)

\(=\frac{19}{17}.\frac{51}{76}\)

\(=\frac{19.51}{17.76}\)

\(=\frac{19.17.3}{17.19.4}\)

\(=\frac{3}{4}\)

_{Làm ơn giúp mình với !}

a) 12 : { 400 : [ 500 - ( 125 + 25 . 7 )]}

= 12 : { 400 : [ 500 - ( 125 + 175 )]}

= 12 : { 400 : [ 500 - 300 ]}

= 12 : { 400 : 200 }

= 12 : 2 

= 6

b) 5 . 22 - 18 : 3

= 110 - 6

= 104

c) 18 : 3 + 182 + 3 . ( 51 : 17 )

= 6 + 182 + 3.3

= 6 + 182 + 9

= 197

d) 25.8 - 12.5 + 170 : 17 - 8

= 1000 - 60 + 10 - 8

= 940 + 10 - 8

= 940 + 2

= 942

17/15>29/32

12/18<13/17

16/51>31/96

21/25>19/29>60/81

e

, 11-12 +13-14 +15-16 +17-18+19-20

= (11-12) +(13-14) +(15-16) +(17-18) +(19-2)

= - 1 . 4 + (19-2)

= 4 + 17

= 21

e,-5

f,-200

e)Ta có 11-12+13-14+15-16+17-18+19-20

         =(11-12)+(13-14)+(15-16)+(17-18)+(19-20)   

         =  (-1)    +   (-1)   +   (-1)   +   (-1)   +    (-1)

         =   (-1) . 5

         = -5

f)  Ta có -3752-(29-3632)-51

             = -3752-29+3632-51

             = -100-29-51

             = -129     -51

            =-180 

a) = 13/60

b) =27/5 hoặc 5,4

c) = 77/20 hoặc 3,85

k cho mình nha