a) (2/5 x 25/29) + (3/5 x 25/29)
= (50/145) + (75/145)
= 125/145

b) (5/2 x 3/7) - (3/14 : 6/7)
= 15/14 - (3/14 x 7/6)
= 15/14 - 1/2
= (30/28) - (14/28)
= 16/28
= 4/7

c) (15/4 : 5/12) - (6/5 : 11/15)
= (15/4 x 12/5) - (6/5 x 15/11)
= 180/20 - 90/55
= 9 - 18/11
= (99/11) - (18/11)
= 81/11
= 7 4/11

a) (2/3) + (20/21 x 3/2 x 7/5)
= 2/3 + (60/210)
= 2/3 + 2/7
= (14/21) + (6/21)
= 20/21

b) (5/17 x 21/32 x 47/24 x 0)
= 0

c) (11/3 x 26/7) - (26/7 x 8/3)
= (286/21) - (208/21)
= 78/21
= 3 9/21
= 3 3/7

a) (25/8) : x = 5/16
=> (25/8) x (16/5) = x
=> 4 = x

b) x + (7/15) = 6/15
=> x = (6/15) - (7/15)
=> x = -1/15

c) x : (28/49) = 7/12
=> x x (49/28) = 7/12
=> x = (7/12) x (28/49)
=> x = 1/2

a) 6 x x = (5/8) : (3/4)
=> 6x = (5/8) x (4/3)
=> 6x = 20/24
=> 6x = 5/6
=> x = (5/6) / 6
=> x = 5/36

câu,b,không,đủ,thông,tin,nhan,bạn.

\(a.\)

\(\dfrac{-28}{35}=\dfrac{16}{x}\)

\(\Rightarrow x=\dfrac{35\cdot16}{-28}=\dfrac{5\cdot7\cdot4\cdot4}{-7\cdot4}=-20\)

\(b.\)

\(\dfrac{x+7}{15}=\dfrac{-24}{36}\)

\(\Rightarrow x+7=\dfrac{15\cdot-24}{36}=\dfrac{5\cdot3\cdot-12\cdot2}{12\cdot3}=-10\)

\(\Leftrightarrow x=-17\)

a: =>16/x=-4/5

hay x=-20

b: =>x+7/15=-2/3

=>x+7=-10

hay x=-17

Bài 2: 

\(=\dfrac{28}{25}\cdot\dfrac{15}{7}\cdot5=\dfrac{75}{25}\cdot4=12\)

Bài 1: 

a: \(x+\dfrac{7}{8}=\dfrac{13}{2}:4=\dfrac{13}{8}\)

nên x=13/8-7/8=6/8=3/4

b: \(x:\dfrac{5}{3}=\dfrac{6}{5}-\dfrac{2}{3}=\dfrac{18-10}{15}=\dfrac{8}{15}\)

nên \(x=\dfrac{8}{15}\cdot\dfrac{5}{3}=\dfrac{8}{9}\)

1. a, 35x67+35x33=35x100=3500

b,8x39x125=8x125x39=1000x39=39000

5. a, ( -15)-|-7|=(-15)-7=-18

b, |-15|-|18|=15-18=-3

X+(-72)=(-28)+(-72)=-100

1.thực hiện phép tính ( hợp lý nếu có thể)         
a) 35. 67 + 35. 33 = 35 . ( 67 + 33 ) = 33 . 100 = 3300            

b) 8.39.125 = ( 8 . 125 ) . 39 = 1000 . 39 = 39000           
a) 3.(15 − 5)2 − 215: 213 = 3.10.2-215:213 = 60 - 1,00... = (bạn tự tính)     

b) 2.(3.52 – 12) =2.(156-12)=2.144=288

c) 52 − 24 : 23 =52-1,043478261 =51,043478261    
a )2340 : [5. 89 - (125 + 5 . 72) + 5 . 11]  

= 2340 : [445-(125+360)+55]

= 2340 : [445-485+55]

= 2340:15

=156

b) 30: {20- [5 + (5 – 2 )2]}=30:{20-[5+3.2]}=30:{20-11}=30:9=3,(3)
a) (−7) + (− 5) =-12

b) 2013 + [ 340 + ( − 2013)]=2013+340+(-2013)=[2013+(-2013)]+340=0+340=340   
a) (– 15) – | − 7 |;      =-15-7=-22

b) | − 15| − | 18 | =15-18=-3
Tính giá trị của biểu thức: x + (−72), biết x = − 28.

Thay x=-28 vào x+(-72) ta được:

=> -28+(-72)=-100