a ) 1/4 x X x 2 = 15

X x 2 = 1/4 x 15

Xx2=3,75

x= 3,75 : 2

x= 1,875

a) 1/4.x+x=36,5-21,5

    1/4.x+x=15

   x.(1/4+1)=15

   x.5/4      =15

   x            =15:5/4

   x            =12

b) 3/5.x+x.2=53-40

    3/5.x+x.2=13

     x.(3/5+2)=13

     x.13/5    =13

     x            =13:13/5

     x            =5

\(x\times\frac{3}{5}+x:5=\frac{2}{3}\)

\(x\times\frac{3}{5}+x\times\frac{1}{5}=\frac{2}{3}\)

\(\frac{3}{5}x+\frac{1}{5}x=\frac{2}{3}\)

\(\frac{4}{5}x=\frac{2}{3}\)

\(x=\frac{4}{5}:\frac{2}{3}\)

\(x=\frac{6}{5}\)

Phần b tương tự.

mot oto di mot quang duong trong 3 gio gio thu nhat di duoc 1/4 quang duong , gio thu hai di duoc 2/5 quang duong do , Hoi gio thu ba oto di duoc may phan quang duong do ?

A = 4 . 2 . 25 . 5 . 175 

A = 2² . 2 . 5² . 5 . 5² . 7 

A = 2²⁺¹ . 5²⁺¹⁺² . 7  

A = 2³ . 5⁵ .7

A = 175000

\(B=4^2-10^4:\left(50\cdot273-50\cdot73\right)\)

\(B=4^2-10^4:\left[50\cdot\left(273-73\right)\right]\)

\(B=4^2-10^4:\left(50\cdot200\right)\)

\(B=4^2-10^4:10^4=4^2-1=15\)

\(C=3\times53\times6+2\times9\times87-18\times40\)

\(C=18\times53+18\times87-18\times40\)

\(C=18\times\left(53+87-40\right)\)

\(C=18\times100=1800\)

a, 53 x 39 + 47 x 39 - 53 x 21 - 47 x 21

= 53 x (39-21) + 47 x (93-21)

=53 x 18 + 47 x 18

= (53 +47) x 18

=100 x 18

=1800

b,2 x 53 x 12 + 4 x 6 x 87 - 3 x 8 x 40

=24 x 53 + 24 x 87 - 24 x 40

=24 x (53+87-40)

=24 x 100

=2400

c,5 x 7 x 77 - 7 x 60 +49 x 25 -15 x 42.

=5 x 7 x 77 - 7 x 5 x 12 +49 x 5 x 5 - 5 x 3 x 42.

=5 x 539 - 84 x 5 +245 x 5 -5 x 126

=5 x (539 - 84 +245 -126)

=5 x 574

=2870

tính nhanh cơ

a, 53 x 39 + 47 x 39 ‐ 53 x 21 ‐ 47 x 21
= 53 x ﴾39‐21﴿ + 47 x ﴾93‐21﴿
=53 x 18 + 47 x 18
= ﴾53 +47﴿ x 18
=100 x 18
=1800
b,2 x 53 x 12 + 4 x 6 x 87 ‐ 3 x 8 x 40
=24 x 53 + 24 x 87 ‐ 24 x 40
=24 x ﴾53+87‐40﴿
=24 x 100
=2400
c,5 x 7 x 77 ‐ 7 x 60 +49 x 25 ‐15 x 42.
=5 x 7 x 77 ‐ 7 x 5 x 12 +49 x 5 x 5 ‐ 5 x 3 x 42.
=5 x 539 ‐ 84 x 5 +245 x 5 ‐5 x 126
=5 x ﴾539 ‐ 84 +245 ‐126﴿
=5 x 574
=2870

Mi Su

x + 21/40 = 53/40

x = 53/40 - 21/40

x = 32/40 = 4/5

34/35 : x = 17/5

x = 34/35 : 17/5

x = 2/7

`x + 3 / 4 xx 7 / 10 = 53 / 40`

`x + 21 / 40 = 53 / 40`

`x = 53 / 40 - 21 / 40`

`x = 32 / 40`

`x = 4 / 5`

____________________________

`( 2 / 5 + 4 / 7 ) : x = 17 / 5`

`( 14 / 35 + 20 / 35 ) : x = 17 / 5`

`34 / 35 : x = 17 / 5`

`x = 34 / 35 : 17 / 5`

`x = 34 / 35 xx 5 / 17`

`x = 2 / 7`

x + 3/4 x 7/10 = 53/40

x + 21/40 = 53/40

x = 53/40 - 21/40 

x = 4/5

(2/5 + 4/7) : x = 17/5

34/35 : x = 17/5

x = 34/35 : 17/5

x = 2/7

Bạn dùng tính chất phân phối, giao hoán để làm nhé

A+0   B=2400   c=420

1) a) 53 x 39 + 47 x 39 - 53 x 21 - 47 x 21

= 39 x (53 + 47) - 21 x (53 - 47)

= 39 x 100 - 21 x 6

= 3900 - 126

= 3774

b) 2 x 53 x 12 + 4 x 6 x 87 - 3 x 8 x 40

= 1272 + 2088 - 960

= 3360 - 960

= 2400

c) 5 x 7 x 77 - 7 x 60 + 47 x 25 - 15 x 42

= 2695 - 420 + 1175 - 630

= 2275 + 545

= 2820

2) a) x : [(1800 + 600) : 30] = 560 : (315 - 35)

                     x : (2400 : 30) = 560 : 280

                                  x : 80 = 2

                                         x = 2 x 80

                                    => x = 160

b) [(250 - 25) : 15] : x = (450 - 60) : 130

                225 : 15 : x = 390 : 130

                         15 : x = 3

                               x  = 15 : 3

                           => x = 5

Học tốt!!!