a, 64 x 7 + 81 x 93 + 17 x 7

= 7 x ( 64 + 17 ) + 81 x 93

= 7 x 81 + 81 x 93

= 81 x ( 93 + 7 )

= 81 x 100

= 8100

a) 64 x 7 + 81 x 93 + 17 x 7

= 7 x ( 64 + 17 ) + 81 x 93

= 7 x 81 + 81 x 93

= 81 x ( 7 + 93 )

= 81 x 100

= 8100

14 x 32 + 7x 140 - 28

= 14 x 32 + 7 x 14 x 10 - 14 x 2

= 14 x 32 + 14 x 70 - 14 x 2

= 14 x ( 32 + 70 - 2 )

= 14 x 100

= 1400

17 x 35 + 67 x 17 - 34

= 17 x 35 + 67 x 17 - 2 x 17

= 17 x ( 35 + 67 - 2 )

= 17 x 100

= 1700

17 x 35 + 67 x 17 - 34

= 17 x (35 + 67) - 34

= 17 x 102 - 34

= 1734 -  34

= 1700

\(37\times46+37\times51+111\)

\(=37\times46+37\times51+37\times3\)

\(=37\times\left(46+51+3\right)\)

\(=37\times100\)

\(=3700\)

------------

\(172\times47+86\times8-34\times4\)

\(=172\times47+172\times4-34\times4\)

\(=172\times\left(47+4\right)-34\times4\)

\(=172\times51-34\times4\)

\(=172\times3\times17-17\times2\times4\)

\(=17\times\left(172\times3-2\times4\right)\)

\(=17\times\left(516-8\right)\)

\(=17\times508\)

\(=8636\)

------------

\(35\times215-35\times200-175\)

\(=35\times215-35\times200-35\times5\)

\(=35\times\left(215-200-5\right)\)

\(=35\times10\)

\(=350\)

------------

\(48\times56+28\times104\)

\(=48\times2\times28+28\times104\)

\(=28\times\left(48\times2+104\right)\)

\(=28\times200\)

\(=5600\)

88 800

261 304

 x - (28 - x) = x - 24x−(28−x)=x−24.

a) 5 13 + − 5 7 + − 20 41 + 8 13 + − 21 41 = 5 13 + 8 13 + − 20 41 + − 21 41 + − 5 7 = − 5 7

b) 1 28 + − 1 14 + 3 28 + − 1 7 + 3 14 = 1 28 + 3 28 + − 1 14 + 3 14 + − 1 7 = 1 7

c)  1 2 + − 2 3 + 3 4 + − 4 5 + 5 6 + − 5 6 + 4 5 + − 3 4 + 2 3 + − 1 2 = 1 2 + − 1 2 + 3 4 + − 3 4 + − 4 5 + 4 5 + 5 6 + − 5 6 = 0

Bài 3a) 576 + 678 + 780 - 475 - 577 - 679

= ( 578 - 475 ) + ( 678 - 577 ) + ( 780 - 679 )

= 103 + 101 + 101

= 305

b) ( 126 + 32 ) x ( 18 - 16 - 2 ) 

= 158 x 0 

= 0 

c) 36 x 17 + 12 x 34 + 6 x 30 

= 6 x 6 x 17 + 6 x 2 x 34 + 6 x 30

= 6 x 102 + 6 x 68 + 6 x 30

= 6 x ( 102 + 68 + 30 )

= 6 x 200

= 1200

Bài 4:a. x × 6 = 3048 : 2

x × 6 = 1524

x = 1524 : 6

x = 254

b. 56 : x = 1326 – 1318

56 : x = 8

x = 56 : 8

x = 7

a) \(37\times46+37\times51+111\)

\(=37\times46+37\times51+37\times3\)

\(=37\times\left(46+51+3\right)\)

\(=37\times100\)

\(=3700\)

b) \(35\times215-35\times210-175\)

\(=35\times215-35\times210-35\times5\)

\(=35\times\left(215-210-5\right)\)

\(=35\times0\)

\(=0\)

c) \(172\times47+86\times8-34\times4\)

\(=4\times\left(43\times47+86\times2-34\right)\)

\(=4\times\left(2021+172-34\right)\)

\(=4\times2159\)

\(=8636\)

d) \(48\times56+28\times104\)

\(=48\times56+56\times52\)

\(=56\times\left(48+52\right)\)

\(=56\times100\)

\(=5600\)

a) 2x + 25 = 145
\(\Rightarrow\)2x = 145 - 25
\(\Rightarrow\)2x = 120
\(\Rightarrow\)x = 60
b) 216 : x + 34 : x = 10
\(\Rightarrow\)( 216 + 34) : x = 10
\(\Rightarrow\)250 : x = 10
\(\Rightarrow\)x = 250 : 10
\(\Rightarrow\)x = 25
c) 2017 : x - 17 : x = 1000
\(\Rightarrow\)( 2017 - 17 ) : x = 1000
\(\Rightarrow\)2000 : x = 1000
\(\Rightarrow\)x = 2000 : 1000
\(\Rightarrow\)x = 2
d) 4057 + (2x : 38 ) = 20395 
\(\Rightarrow\)2x : 38 = 20395 - 4057
\(\Rightarrow\)2x : 38 = 16338 
\(\Rightarrow\)2x = 16338 . 38 
\(\Rightarrow\)2x = 620844
\(\Rightarrow\)x = 620844 : 2
\(\Rightarrow\)x = 310422
e) ( x + 1 ) + ( x + 4 ) + ( x + 7 ) + ... + ( x + 28 ) = 155 ( có 10 số hạng x )
\(\Rightarrow\)x + 1 + x + 4 + x + 7 + ... + x + 28 = 155
\(\Rightarrow\)10x + ( 1 + 4 + 7 + ... + 28 ) = 155
\(\Rightarrow\)10x + 145 = 155 
\(\Rightarrow\)10x = 155 - 145
\(\Rightarrow\)10x = 10
\(\Rightarrow\)x = 1

a, x=60

b, x=24

c, x=2

=\(\frac{17}{25}\)