Bài 1 :

a, $\frac{-1}{39}$ + $\frac{-1}{52}$= $\frac{-7}{156}$

b, $\frac{-6}{9}$+ $\frac{-12}{16}$= $\frac{-2}{3}$+ $\frac{3}{4}$ = $\frac{-17}{12}$

c, $\frac{-2}{5}$- $\frac{-3}{11}$= $\frac{-7}{55}$ 

d, $\frac{-5}{12}$ + 0,75= $\frac{1}{3}$ 

e, $\frac{5}{7}$ . 12$\frac{1}{2}$ -$\frac{5}{7}$ . 5$\frac{1}{2}$ = $\frac{5}{7}$.(6- $\frac{5}{2}$) = $\frac{5}{7}$ - $\frac{7}{2}$ =$\frac{-39}{14}$ 

Bài 2 :

a, A = 2/3 + 3/4 (-4/9)

A= 17/12 . (-4/9)

A= -17/27

b, B= -3/4 . 5 3/13 - 0,75 - 36/13

B = -3/4 . 15/13 - 3/4. 36/13

B = (36/13 . -3/4) - ( 15/13 . 3/4)

B = -27/13 - 45/92

c, C = ( 3/4 - 0,2) . (0,2-4/5)

C= (3/4 - 1/5) . ( 1/5 - 4/5)

C= 11/20 . (-3/5)

C = -33/100

II. Dạng 2 tìm x

Bài 1

a, x + 13/10 = -2/15 

x = -2/15 - 13/10

x= -12/30

b, x + 5/6 = 2/5 - (-2/3)

x + 5/6 = 16/15

x = 16/15 - 5/6 

x = 7/30

c, 13/20 + (3/5 - x) = 5/8

13/20 + x = 5/8 + 3/5

13/20 + x = 49/40

x = 49/40 - 13/20

x  = 23/40

Bài 2 :

a, x : 3/8 = -131 /33

x = -131/33 . 3/8

x = -131/88

@byklinh321

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