4/9 x 3/8 + 5/8 = 1/6 + 5/8 = 19/24

1/3 : 1/6 - 5/11 = 2 - 5/11 = 17/11

1/6 : 1/4 x 9/8 = 2/3 x 9/8 = 3/4

Cái này là phân số hay phép chia vậy bạn

\(\dfrac{4}{9}\) x \(\dfrac{3}{8}\) + \(\dfrac{5}{8}\) = \(\dfrac{1}{6}\) + \(\dfrac{5}{8}\) = \(\dfrac{19}{24}\)

\(\dfrac{1}{3}\) : \(\dfrac{1}{6}\) - \(\dfrac{5}{11}\) = 2 - \(\dfrac{5}{11}\) = \(\dfrac{17}{11}\)

\(\dfrac{1}{6}\) : \(\dfrac{1}{4}\) x \(\dfrac{9}{8}\) = \(\dfrac{2}{3}\) x \(\dfrac{9}{8}\) = \(\dfrac{3}{4}\)

 a,    2 \(\times\) \(\dfrac{2}{4}\) : \(\dfrac{4}{5}\)                                  b, \(\dfrac{7}{8}\) \(\times\) \(\dfrac{4}{5}\) : 3

=              1 :  \(\dfrac{4}{5}\)                              =      \(\dfrac{7}{10}\)       : 3

=              1 \(\times\) \(\dfrac{5}{4}\)                            =         \(\dfrac{7}{10}\)  \(\times\) \(\dfrac{1}{3}\)

=                 \(\dfrac{5}{4}\)                               =            \(\dfrac{7}{30}\)

\(2\times\dfrac{2}{4}:\dfrac{4}{5}\)

\(=1:\dfrac{4}{5}\)

\(=1\times\dfrac{5}{4}\)

\(=\dfrac{5}{4}\)

__________________________

\(\dfrac{7}{8}\times\dfrac{4}{5}:3\)

\(=\dfrac{7}{2}\times\dfrac{1}{5}:3\)

\(=\dfrac{7}{10}\times\dfrac{1}{3}\)

\(=\dfrac{7}{30}\)

 Chúc bạn học tốt:>

Lời giải:

a.

$\frac{5}{15}-\frac{1}{6}\times \frac{2}{5}=\frac{5}{15}-\frac{1}{15}=\frac{4}{15}$

b.

$\frac{8}{24}+\frac{3}{4}:\frac{1}{8}=\frac{1}{3}+6=\frac{19}{3}$

c.

$\frac{1}{7}: \frac{2}{8}-\frac{1}{7}=\frac{1}{7}\times 4-\frac{1}{7}$

$=\frac{1}{7}\times (4-1)=\frac{1}{7}\times 3=\frac{3}{7}$

\(=\frac{47}{40}:\frac{3}{4}=\frac{47}{40}\times\frac{4}{3}=\frac{188}{120}=1\frac{68}{120}\)

\(\frac{4}{5}+\frac{3}{8}:\frac{3}{4}=\frac{4}{5}+\frac{1}{2}=\frac{13}{10}\)

Nhân, chia trước cộng, trừ sau nhé !

a: \(=\dfrac{3}{5}\cdot\dfrac{5}{4}+\dfrac{1}{2}\cdot\dfrac{2}{3}=\dfrac{3}{4}+\dfrac{1}{3}=\dfrac{9+4}{12}=\dfrac{13}{12}\)

b: \(\Leftrightarrow x\cdot\dfrac{5}{4}=\dfrac{5}{8}\)

hay x=1/2

\(A=\dfrac{5}{4}-\left(\dfrac{3}{8}+\dfrac{1}{a}\right):\dfrac{4}{5}\) \(\left(a\ne0\right)\)

Tại a = 12 biểu thức \(A=\dfrac{5}{4}-\left(\dfrac{3}{8}+\dfrac{1}{12}\right):\dfrac{4}{5}=\dfrac{5}{4}-\dfrac{11}{24}:\dfrac{4}{5}=\dfrac{5}{4}-\dfrac{11}{24}.\dfrac{5}{4}=\dfrac{5}{4}-\dfrac{55}{96}=\dfrac{65}{96}\)

Để \(A=\dfrac{15}{23}< =>\dfrac{5}{4}-\left(\dfrac{3}{8}+\dfrac{1}{a}\right):\dfrac{4}{5}=\dfrac{15}{23}\)

\(\Leftrightarrow\left(\dfrac{3}{8}+\dfrac{1}{a}\right):\dfrac{4}{5}=\dfrac{55}{92}< =>\dfrac{3}{8}+\dfrac{1}{a}=\dfrac{11}{23}< =>\dfrac{1}{a}=\dfrac{19}{184}< =>a=\dfrac{184}{19}\)

Thay \(a=12\) vào A ta có:

\(A=\dfrac{5}{4}-\left(\dfrac{3}{8}+\dfrac{1}{12}\right):\dfrac{4}{5}=\dfrac{65}{96}\)

Vậy:

____________________

Ta có:

\(A=\dfrac{15}{23}\) khi \(\dfrac{5}{4}-\left(\dfrac{3}{8}+\dfrac{1}{a}\right):\dfrac{4}{5}=\dfrac{15}{23}\)

\(\Rightarrow\left(\dfrac{3}{8}+\dfrac{1}{a}\right)\cdot\dfrac{5}{4}=\dfrac{5}{4}-\dfrac{15}{23}\)

\(\Rightarrow\dfrac{3}{8}+\dfrac{1}{a}=\dfrac{55}{92}:\dfrac{5}{4}\)

\(\Rightarrow\dfrac{3}{8}+\dfrac{1}{a}=\dfrac{11}{23}\)

\(\Rightarrow\dfrac{1}{a}=\dfrac{11}{184}\)

\(\Rightarrow a=\dfrac{1\cdot184}{11}=\dfrac{184}{11}\)