9720:216 x 25 + 801,7 

= 45 x 25 + 801,7

= 1125 + 801,7

= 1926,7

    56,7 + 48x 56 : 112

= 56,7 + 2688:112

=56,7 + 24

= 80,7

bạn ơi cái phép mà 1 á là mình viết là 216 chứ ko phải 2116 nha

2,4 x 45,6 + 2,4 x 53,1 + 2,4 x 1,3

2,4 x ( 45,6 + 53,1 + 1,3 )

2,4 x 100

240

240 nhé

=2,4 x (45,6 + 51,3 + 1,3)

=2,4 x 100

=240

58 x 120 - 20 x 58

= 58 x ( 120 - 20 )

= 58 x 100 

= 5800

\(58\times120-20\times58\)

\(=58\times\left(120-20\right)\)

\(=58\times100\)

\(=5800\)

58 x 120-20 x58

=58 x (120-20)

=58.100=5800

Bài 2: 

a: =47,4+47,4x4=47,4x5=237

b: =(0,26+0,74)+(0,41+0,59)=1+1=2

Tính bằng cách thuận tiện ( đề `b` )

`13/50+74/100+41/100+59/100`

`=>` `26/100+74/100+41/100+59/100`

`=>` `(26/100+74/100) + ( 41/100 + 59/100)`

`=>` `1+1`

`=>` `2`

tính nhanh:

`a,` \(2 × 4 × 8 × 0 , 5 × 0 , 125 × 0 , 25 × ( 0 , 4321 + 0 , 5679 )\)

`=>`\( 2 × 4 × 8 × 0 , 5 × 0 , 125 × 0 , 25 × 1\)

`=>`\(( 2 × 0 , 5 ) × ( 4 × 0 , 25 ) × ( 8 × 0 , 125 ) × 1\)

`=>`\( 1 × 1 × 1 × 1=1\)

= ( 101 x 37 x 50 - 101 x 50 x 36 ) : ( 1 + 2 + 3 + ............. + 100 )

= ( 101 x 1850 - 101 x 1800 ) : ( 1 + 2 + 3 + ............. + 100 )

= [ 101 x ( 1850 - 1800 )] : ( 1 + 2 + 3 + ............. + 100 )

= [ 101 x 50 ] : ( 1 + 2 + 3 + ............. + 100 )

= 5050 : 5050

= 1

 T - I - C - K mk nha 

chúc bạn học tốt ~

a) 3/7 + 4/9 + 4/7 + 5/9

= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )

= 7/7 + 9/9

= 1  + 1 

= 2

b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45

= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5

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

= 2 + 2 + 2 + 2 + 1

= 2  x 4 + 1

= 8  +1 

= 9

c)  1/8 + 1/12 + 3/8 + 5/12

= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)

= 4/8 + 6/12

= 1/2 + 1/2

= 2/4 = 1/2

mỏi tay rồi

d; (1 - \(\dfrac{1}{2}\)) x (1 - \(\dfrac{1}{3}\)) x (1 - \(\dfrac{1}{4}\)) x ... x ( 1 - \(\dfrac{1}{100}\))

 = \(\dfrac{1}{2}\) x \(\dfrac{2}{3}\)  x \(\dfrac{3}{4}\) x \(\dfrac{3}{4}\) x ... x \(\dfrac{99}{100}\)

= \(\dfrac{1}{100}\)

e; \(\dfrac{9}{5}\) : \(\dfrac{17}{15}\) + \(\dfrac{8}{5}\) : \(\dfrac{17}{15}\)

=  \(\dfrac{9}{5}\) x \(\dfrac{15}{17}\) + \(\dfrac{8}{5}\) x \(\dfrac{15}{17}\)

=  \(\dfrac{27}{17}\) + \(\dfrac{24}{17}\)

=  \(\dfrac{51}{17}\)

=   3

\(A=20\times21+21\times22+...+99\times100\)

\(3\times A=20\times21\times\left(22-19\right)+21\times22\times\left(23-20\right)+...+99\times100\times\left(101-98\right)\)

\(=20\times21\times22-19\times20\times21+...+99\times100\times101-98\times99\times100\)

\(=99\times100\times101-19\times20\times21\)

Suy ra \(A=\frac{99\times100\times101-19\times20\times21}{3}=360640\)

\(B=3\times4\times5+4\times5\times6+...+98\times99\times100\)

\(4\times B=3\times4\times5\times\left(6-2\right)+4\times5\times6\times\left(7-3\right)+...+98\times99\times100\times\left(101-97\right)\)

\(=3\times4\times5\times6-2\times3\times4\times5+...+98\times99\times100\times101-97\times98\times99\times100\)

\(=98\times99\times100\times101-2\times3\times4\times5\)

Suy ra \(B=\frac{98\times99\times100\times101-2\times3\times4\times5}{4}=24497520\)

Tính nhanh :

165 x 23 - 65 x 23

= 23 x ( 165 - 65 )

= 23 x 100

= 2300                    

136 + 63 + 100

= 199 + 100

= 299                     

165 -20 - 65

= ( 165 - 65 ) - 20

= 100 - 20

= 80

165 x 23 - 65 x 23 = ( 165 - 65 ) x 23 = 100 x 23 = 2300

136 + 63 + 100 = 199 + 100 = 299

165 - 20 - 65 = 165 - 65 - 20 = 100 - 20 = 80

165 x 23 - 65 x 23 

= ( 165 - 65 ) x 23

= 100 x 23

= 2300

      136 + 63 + 100

    = 199 + 100

    = 299

165 - 20 - 65

= ( 165 - 65 ) - 20

= 100 - 20 

= 80

              ~~~ Hok tốt~~~