a. C1: \(\dfrac{8}{15}.\dfrac{5}{6}=\dfrac{4}{9}\)

C2: \(\dfrac{2}{3}.\dfrac{4}{5}.\dfrac{5}{6}=\dfrac{2.4.5}{3.5.3.2}\)

Triệt tiêu phần giống nhau ở tử và mẫu ta có 

\(=\dfrac{4}{9}\)

b. \(C1:\left(\dfrac{1}{2}+\dfrac{1}{3}\right).\dfrac{1}{5}=\dfrac{5}{6}.\dfrac{1}{5}=\dfrac{1}{6}\)

C2: \(\dfrac{1}{2}.\dfrac{1}{5}+\dfrac{1}{3}.\dfrac{1}{5}=\dfrac{1}{10}+\dfrac{1}{15}=\dfrac{1}{6}\)

Cách 1:

$(\frac{2}{3}\times \frac{4}{5})\times \frac{5}{6}=\frac{8}{15}\times \frac{5}{6}=\frac{8\times 5}{15\times 6}=\frac{2\times 2\times 2\times 5}{3\times 5\times 2\times 3}=\frac{4}{9}$

Cách 2:

$(\frac{2}{3}\times \frac{4}{5})\times \frac{5}{6}=\frac{2}{3}\times (\frac{4}{5}\times \frac{5}{6})=\frac{2}{3}\times \frac{4}{6}=\frac{2\times 4}{3\times 6}=\frac{2\times 4}{3\times 2\times 3}=\frac{4}{9}$

Cách 1:

$(\frac{1}{2}+\frac{1}{3})\times \frac{1}{5}=\left(\frac{3+2}{6}\right)\times \frac{1}{5}=\frac{5}{6}\times \frac{1}{5}=\frac{1}{6}$

Cách 2:

$(\frac{1}{2}+\frac{1}{3})\times \frac{1}{5}=\frac{1}{2}\times \frac{1}{5}+\frac{1}{3}\times \frac{1}{5}=\frac{1}{10}+\frac{1}{15}=\frac{3}{30}+\frac{2}{30}=\frac{5}{30}=\frac{1}{6}$

Giải đấy đủ giúp mình với 

a: =8/15x1/4=2/15

b: \(=\dfrac{5}{3}\cdot\dfrac{4}{5}\cdot\dfrac{6}{7}=\dfrac{24}{21}=\dfrac{8}{7}\)

c: \(=\dfrac{2}{5}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=\dfrac{2}{5}\)

(2/3 x 4/5) x 5/6

=   8/15     x 5/6

=             4/9

(2/3 x 4/5) x 5/6 

= (5/6 x 4/5) x 2/3

=        2/3     x 2/3

=              4/9

(1/2 + 1/3) x 1/5

=   5/6        x 1/5

=               1/6

(1/2 + 1/3) x 1/5

= (1/2 x 1/5) + (1/3 x 1/5)

=       1/10    +        1/15

=                 1/6

4A6?

Đây bạn nhé

5,5 + \(\dfrac{3}{4}\) - 5 + \(\dfrac{1}{4}\)

(5,5 - 5) + (\(\dfrac{3}{4}\) + \(\dfrac{1}{4}\))

= 0,5  + 1

= 1,5 

\(\dfrac{5}{2}\) x  \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) : \(\dfrac{3}{2}\)

= \(\dfrac{5}{2}\) x \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) x \(\dfrac{2}{3}\)

=  (\(\dfrac{5}{2}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)

= (\(\dfrac{10}{4}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)

= \(\dfrac{11}{4}\) x \(\dfrac{2}{3}\)

= \(\dfrac{11}{6}\) 

Tính \(x\): 

  435  - [\(x\) + 16] = 425 : 17

  435 - [\(x\) + 16] = 25

          [\(x\) + 16] = 435 - 25

           \(x\) + 16 = 410

           \(x\)        = 410 - 16

          \(x\)         = 394

a) Cách 1 : (3/4 + 1/2) x 5/7

               = 5/4 x 5/7

                = 25/28

Cách 2 : (3/4 + 1/2) x 5/7

           = 3/4 x 5/7 + 1/2 x 5/7

            = 15/28 + 5/14

            = 25/28

b) Cách 1 : 5/7 x 13/21 + 2/7 x 13/21

= 65/147 + 26/147

= 13/21

Cách 2 : 5/7 x 13/21 + 2/7 x 13/21

= (5/7 + 2/7) x 13/21

= 1 x 13/21

= 13/21

câu c tự làm

8 /15 :2/3+7/15:2/3 =                                              tính bằng 2 cách nhé các bạn

2 năm sau mày sẽ chết do dịch bệnh

a.\(\dfrac{2}{3}\times\dfrac{4}{9}+\dfrac{2}{3}\times\dfrac{5}{9}=\dfrac{2}{3}\times\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{2}{3}\times1=\dfrac{2}{3}\)

b.\(\dfrac{7}{5}\times\dfrac{3}{4}-\dfrac{1}{2}\times\dfrac{3}{4}=\dfrac{3}{4}\times\left(\dfrac{7}{5}-\dfrac{1}{2}\right)=\dfrac{3}{4}\times\dfrac{9}{10}=\dfrac{27}{40}\)

c.\(\left(\dfrac{5}{6}+\dfrac{5}{8}\right)\times\dfrac{2}{3}=\dfrac{35}{24}\times\dfrac{2}{3}=\dfrac{35}{36}\)

a) 2/3 x 4/9 + 2/3 x 5/9 

=2/3 x ( 4/9 + 5/9)

= 2/3 x 1

=  2/3

b, 7/5 x 3/4 - 1/2 x 3/4

= ( 7/5 - 1/2 ) x 3/4

=     9/10         x 3/4

=         21/40

c, ( 5/6 + 5/8 ) x 2/3       

 =      35/24 x 2/3

=       35/36

\(5\dfrac{3}{4}:3+2\dfrac{1}{4}\times\dfrac{1}{3}-\dfrac{1}{8}=\left(5\dfrac{3}{4}+2\dfrac{1}{4}\right)\times\dfrac{1}{3}-\dfrac{1}{8}\\ =8\times\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{8}{3}-\dfrac{1}{8}=\dfrac{61}{24}\\ ----\\ \dfrac{3}{5}:\dfrac{5}{6}:\dfrac{6}{7}:\dfrac{7}{8}+\dfrac{2}{5}+\dfrac{23}{35}\\ =\dfrac{3}{5}\times\dfrac{6}{5}\times\dfrac{7}{6}\times\dfrac{8}{7}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{18}{25}\times\dfrac{4}{3}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{353}{175}\)