a) 20 x 190 x 50

= 20 x 50 x 190

= 1000 x 190

= 190 000

b) 769 x 85 - 769 x 75

= 769 x (85 - 75)

= 769 x 10

= 7690

Tính giá trị của biểu thức bằng cách thuận tiện :

a. 20 x 190 x 50=(20 x 50) x 190

                         = 1000 x 190

                          = 190 000

b. 769 x 85 – 769 x 75= 769 x(85 - 75)

                                   = 769 x 10

                                    = 7690

a) 20 x190 x 50

= 3800 x 50

= 190000

b) 769 x 85 – 769 x 75

= 769 x (85-75)

= 769 x  10

= 7690

giúp mk nhe

nhanh lên nha

190x28-19x190+190

=190x(28-19+1)

=190x10

=1900

a: =13:25=0,25

b: =28+28x8+28=280

\(900\times28:9\\ =\left(900:9\right)\times28\\ =100\times28\\ =2800\)

(900x28):9

=(900:9)x28

=100x28

=2800

\(900\times28:9\)
\(\Rightarrow\left(900:9\right)\times28\)
\(\Rightarrow100\times28\)
\(\Rightarrow2800\)

Câu 4: 

a: =190x1000=190000

b: =7690

câu 2 : 

a) 248735 – x = 139462

x = 248735 – 139462

x = 109273

b) X x 34 = 7446

x = 7446 : 34

x = 219

a) \(\dfrac{3}{5}\times\dfrac{17}{21}+\dfrac{17}{21}\times\dfrac{2}{5}\)

\(=\dfrac{17}{21}\times\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\)

\(=\dfrac{17}{21}\times1\)

\(=\dfrac{17}{21}\)

b) \(\dfrac{15}{8}:\dfrac{5}{20}-\dfrac{7}{8}:\dfrac{1}{4}\)

\(=\dfrac{15}{8}\times\dfrac{20}{5}-\dfrac{7}{8}\times4\)

\(=\dfrac{15}{8}\times4-\dfrac{7}{8}\times4\)

\(=4\times\left(\dfrac{15}{8}-\dfrac{7}{8}\right)\)

\(=4\times1\)

\(=4\)

a, =(3/5+2/5)x17/21

=1x17/21

=17/21

a) \(\dfrac{3}{5}\) x \(\dfrac{17}{21}+\dfrac{17}{21}\) x \(\dfrac{2}{5}\)

\(=\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\) x \(\dfrac{17}{21}\)

\(=\dfrac{5}{5}\) x \(\dfrac{17}{21}\)

\(=1\) x \(\dfrac{17}{21}\)

\(=\dfrac{17}{21}\)

b) \(\dfrac{15}{8}:\dfrac{5}{20}-\dfrac{7}{8}:\dfrac{1}{4}\)

\(=\dfrac{15}{8}:\dfrac{1}{4}-\dfrac{7}{8}:\dfrac{1}{4}\)

\(=\left(\dfrac{15}{8}-\dfrac{7}{8}\right):\dfrac{1}{4}\)

\(=\dfrac{8}{8}:\dfrac{1}{4}\)

\(=1:\dfrac{1}{4}\)

\(=\dfrac{1}{1}:\dfrac{1}{4}\)

\(=\dfrac{1}{1}\) x \(\dfrac{4}{1}\)

\(=\dfrac{4}{1}\)

\(=4\)

a) 35 x 2 x 9 x 5

= (35 x 9) x (2 x 5)

= (35 x 10 - 35) x 10

= (350 - 35) x 10

= 315 x 10 = 3150

b) 24 x 71 + 71 x 75 + 71

= 71 x (24+75+1)

=71 x 100

= 7100

giúpppppppppppppppppppppppppppppppppppp

a, 25+35+76+65+22
=(65+35)+(76+22)+25
=100+100+25
=225
c , 78-23-25
=78-(23+25)
=78-48
=30
a , x-45=20 
x=20+45
x=65
b , 45 - x=20
     x =45-20
     x= 25

Bài 2: 

a: Ta có: x-45=20

nên x=65

b: Ta có: 45-x=20

nên x=25

a, 2 x 9 x 5 x 7 x 4 x 25

= 2³ x 3² x 5³ x 7 

= 63000

b, 6 x 14 x 5 x 25 x 3 x 4

= 2⁴ x 3² x 5³ x 7

= 126000

a) 2x9x5x7x4x25
= (2x5)x(4x25)x(9x7)
= 10x100x63
= 63000
b) 2x14x5x25x3x4
= (2x5)x(4x25)x(14x3)
= 10x100x42
= 42000