a) 1+2+3+4+5+6+7+8+9

= (1+9)+(2+8)+(3+7)+(4+6)+5

= 10+10+10+10=5

= 45

b) 19+28+37+46+81+72+63+54

= (19+81)+(28+72)+(46+54)+(63+37)

= 100+100+100+100

= 400

Bài 2 : Tính nhanh

 a ) ( 8 , 7 x 29 +  8, 7 x 35 ) : 64

= [ 8.7 x ( 29 + 35 ) ] : 64

= [ 8.7 x 64 ] : 64

= 8.7

b ) 372 x 9 + 372

= 372 x ( 9 + 1 )

= 372 x 10

= 3720

c ) 37 x 24 + 37 x 76 + 63  x 79 + 63 x 21

= 37 x ( 24 + 76 ) + 63 x ( 79 + 21 )

= 37 x 100 + 63 x 100

= 100 x ( 37 + 63 )

= 100 x 100

= 10000

d ) 42 x 53 + 47 x 156 - 47 x 114

= 42 x 53 + 47 x ( 156 - 114 )

= 42 x 53 + 47 x 42

= 42 x ( 53 + 47 )

= 42 x 100

= 4200

hok tốt nha 

a) (8,7 x 29 + 8,7 x 35) : 64

= [8,7 x (29 + 35)] : 64

= (8,7 x 64) : 64

= 8,7 x (64 : 64)

= 8,7 x 1 = 8,7

b) 372 x 9 + 372 = 372 x (9 + 1)

= 372 x 10 = 3720

c) 37 x 24 + 37 x 76 + 63 x 79 + 63 x 21

= 37 x (24 + 76) + 63 x (79 + 21)

= 37 x 100 + 63 x 100

= (37 + 63) x 100

= 100 x 100 = 10000

d) 42 x 53 + 47 x 156 - 47 x 114

= 42 x 53 + 47 x (156 - 114)

= 42 x 53 + 47 x 42

= 42  x (53 + 47)

= 42 x 100

= 4200

 a ) ( 8 , 7 x 29 +  8, 7 x 35 ) : 64

= [ 8,7 x ( 29 + 35 ) ] : 64

=  8,7 x 64 : 64

= 8,7

b ) 372 x 9 + 372

= 372 x ( 9 + 1 )

= 372 x 10

= 3720

c ) 37 x 24 + 37 x 76 + 63  x 79 + 63 x 21

= [ 37 x ( 24 + 76 ) ] + [ 63 x ( 79 + 21 ) ] 

= [ 37 . 100 ] + [ 63 x 100 ] 

= 3700 + 6300

= 10000

d ) 42 x 53 + 47 x 156 - 47 x 114
= 42 x 53 + 47 x ( 156 - 114 )
= 42 x 53 + 47 x 42 
= 42 x ( 53 +  47 )
= 42 x 100
= 4200

a/   100 . 37 + 37. 37 + 200 . 63 - 63 . 63\

  =  37 .[ 100+ 37 ]   + 63 . [ 200 - 63 ]  

  =    37. 137             +  63 . 137 

  =    137. [ 37 + 63 ] 

  =   137 . 100 = 13700

b/  84 + 14 .6 + 7 . 12 + 21. 4 + 3.28 

=  84 + 84 +  84 + 84 +84

= 84. 5 = 420 

[ dấu " ." là " x" nha ] đừng quên tích cho tui 

a, 13700

cảm ơn anh NTN và bạn no_nickname nhé ! :))))

a ) 37 x 27 + 63 x 27 

= ( 37 + 63 ) x 27

= 100 x 27

= 2700

b ) 1 + 2 + 3 + 4 + ... + 97 + 98 + 99

= ( 99 - 1 ) : 1 + 1 

= 99 x ( 99 + 1 ) : 2 

= 4950

c ) 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10

= ( 1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + ( 5 + 10 )

= 10 + 10 + 10 + 10 + 15

= 55

37 x 27 x 63 x27

=(37+63)x27

=100 x 27

37 x 27 + 63 x 27

= ( 37 + 63 ) x 27

= 100 x 27

= 2700

1 + 2 + 3 + 4 + ... + 97 + 98 + 99

= ( 1 + 99 ) + ( 2 + 98 ) + .... + ( 51 + 49 ) + 50

= 100 + 100 + ... + 100 + 50   ( có 49 số 100 )

= 100 x 49 + 50

= 4900 + 50

= 4950

1 + 2 + 3 +4 + 5 + 6 +7 + 8 + 9 + 10

= ( 1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + 10 + 5

= 10 + 10 + 10 + 10 +10 + 5

= 10 x 5 + 5

= 55

`4/7+4`

`=4/7+4/1`

`=4/7+28/7`

`=32/7`

__

`3+6/11`

`=33/11+6/11`

`=39/11`

__

`3-5/7`

`=3/1-5/7`

`=21/7-5/7`

`=16/7`

__

`21/9-2`

`=21/9-18/9`

`=3/9`

`=1/3`

__

`15/24+2`

`=15/24+48/24`

`=63/24`

`=21/16`

__

`63/45-20/25`

`=63/45-4/5`

`=63/45-36/45`

`=27/45`

`=9/15`

__

`3/4-2/8`

`=3/4-1/4`

`=2/4`

__

`6/7-5/8`

`=48/56-35/56`

`=13/56`

__

`37/45-5/9`

`=37/45-25/45`

`=12/45`

`=4/15`

__

`46/39-11/13`

`=46/39-33/39`

`=13/39`

`=1/2`

__

`5/12+3/4+1/3`

`=5/12+9/12+4/12`

`=14/12+4/12`

`=18/12`

`=3/2`

__

`1/2+3/7+11/14`

`=7/14+6/14+11/14`

`=13/14+11/14`

`=24/14`

`=12/7`

__

`7/10-(1/5+1/4)`

`=7/10-(4/20+5/20)`

`=7/10-9/20`

`=14/20-9/20`

`=5/20`

`=1/4`

__

`15/4-2/3-3/4`

`=(15/4-3/4)-2/3`

`=12/4-2/3`

`=3-2/3`

`=9/3-2/3`

`=7/3`

a. A = 2 / 3 . 5 + 2 / 5 . 7 + 2 / 7 . 9 + ... + 2 / 37 . 39

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{37}-\frac{1}{39}=\frac{1}{3}-\frac{1}{39}\)

 \(=\frac{13}{39}-\frac{1}{39}=\frac{12}{39}\)

b. B = 4 / 5 . 8 + 4 / 8 . 11 + ... + 4 / 305 . 208 

\(=\frac{4}{3}.\left(\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{305.308}\right)=\frac{4}{3}.\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{305}-\frac{1}{308}\right)\)

 \(=\frac{4}{3}.\left(\frac{1}{5}-\frac{1}{308}\right)=\frac{4}{3}.\frac{303}{1540}=\frac{101}{385}\)

2. a. \(A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{37}-\frac{1}{39}\)

\(=\frac{1}{3}-\frac{1}{39}=\frac{4}{13}\)

b. \(B=\frac{4}{3}.\left(\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{305.308}\right)\)

\(=\frac{4}{3}.\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{305}-\frac{1}{308}\right)\)

\(=\frac{4}{3}.\left(\frac{1}{5}-\frac{1}{308}\right)\)

\(=\frac{4}{3}.\frac{303}{1540}=\frac{101}{385}\)

a) \(A=\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{37\cdot39}\)
\(A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{37}-\frac{1}{39}\)
\(A=\frac{1}{3}-\frac{1}{39}\)
\(A=\frac{12}{39}\)

Bài 2: 

c: \(=x^2\left(x-3\right)-4\left(x-3\right)\)

\(=\left(x-3\right)\left(x-2\right)\left(x+2\right)\)

a.    3, 63 + 5, 13 + 6 , 63 + 8, 13 + 9, 63 + 11 , 13

   = 8,76 + 6 , 63 + 8, 13 + 9, 63 + 11 , 13

   = 15,39 + 8, 13 + 9, 63 + 11 , 13

   = 23,52 + 9, 63 + 11 , 13

   = 33,15 + 11 , 13

   = 44,28

b. 135 , 7 + 20 , 4 + 4 , 6

= 156,1 + 4,6

= 160,7

b)135,7 + (20,4 + 4,6)

    135,7 +         25

           160,7

a) 3,63 + 5,13 + 6,63 + 8,13 + 9,63 + 11,13

=(3,63 + 11 ,13) + ( 5,13 + 9,63 ) + (6,63 +8,13)

=      14,76          +           14,76               +       14,76

= 14 , 76 x 3 

= 44,28

b) 135,7 + 20,4 + 4,6

= 135,7 + (20,4 + 4,6)

= 135,7 +     25

=160,7

A có (99-17)+1=83 phần tử
Số ở giữa sẽ là 17+(82/2) = 58
Những số khác tạo thành các cặp
A=(17+99) + (18+98)+...+58

A=116*(82/2)+58= 4814
Những bài khác tương tự

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