`x . 0,75 + 3/4 . 5 + 2 : 4/3 = 10,5`

`x . 0,75 + 3/4 . 5 + 2 : 4/3 =21/2`

`x. 3/4 + 3/4 . 5 + 2 : 4/3 = 21/2`

`x . 3/4 + 15/4 + 2 xx 3/4 = 21/2`

`x. 3/4 + 21/4=21/2`

`x.3/4 = 21/2 - 21/4`

`x.3/4 = 21/4`

`x=21/4 : 3/4`

`x=21/4 xx 4/3`

`x=21/3`

`x=7`

Vậy `x=7`

\(x\times0,75+\dfrac{3}{4}\times5+2\div\dfrac{4}{3}=10,5\)

\(x\times0,75+\dfrac{15}{4}+2\times\dfrac{3}{4}=10,5\)

\(x\times0,75+\dfrac{15}{4}+\dfrac{6}{4}=10,5\)

\(x\times0,75+\dfrac{21}{4}=10,5\)

\(x\times0,75=\dfrac{21}{4}\)

\(x=7\)

\(\dfrac{6}{7}\times\dfrac{21}{12}\)

\(=\dfrac{6\times3\times7}{7\times2\times6}\)

\(=\dfrac{3}{2}\)

6/7 x 21/12

= 6 x 21/ 7 x 12

= 126/ 84

= 3/2 

`x+3/4=4/3`

`x=4/3-3/4`

`x=16/12 - 9/12`

`x=7/12`

________________

`1/8:x=1/2`

`x=1/8:1/2`

`x=1/8 xx 2`

`x=2/8`

`x=1/4`

______________________

`x-3/11=9/22`

`x=9/22+3/11`

`x=9/22 + 6/22`

`x=15/22`

__________________

`x+1/4 xx 6/7=3/5`

`x+3/14 = 3/5`

`x=3/5-3/14`

`x=27/70`

__________________

`(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`

_____________________

`7/3-x=11/5:5/6`

`7/3-x= 11/5 xx 6/5`

`7/3-x=66/25`

`x=7/3 - 66/25`

`x=-23/75`

a) \(x\) + \(\dfrac{3}{4}\) = \(\dfrac{4}{3}\)                            b) \(\dfrac{1}{8}\) : \(x\) = \(\dfrac{1}{2}\)

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

    \(x\) = \(\dfrac{7}{12}\)                                      \(x\) = \(\dfrac{1}{4}\)

c) \(x\) + \(\dfrac{1}{4}\) x \(\dfrac{6}{7}\) = \(\dfrac{3}{5}\)                    d) \(x\) + \(\dfrac{1}{4}\) x \(\dfrac{6}{7}\) = \(\dfrac{3}{5}\)  

   \(x\) + \(\dfrac{3}{14}\) = \(\dfrac{3}{5}\)                              \(x\) + \(\dfrac{3}{14}\) = \(\dfrac{3}{5}\)

  \(x\) = \(\dfrac{3}{5}\) - \(\dfrac{3}{14}\)                                \(x\) = \(\dfrac{3}{5}\) - \(\dfrac{3}{14}\)

  \(x\) = \(\dfrac{27}{70}\)                                      \(x\) = \(\dfrac{27}{70}\)

e) \(\left(\dfrac{2}{5}+\dfrac{4}{7}\right)\) : \(x\) = \(\dfrac{17}{5}\)             f) \(\dfrac{7}{3}\) - \(x\) = \(\dfrac{11}{5}\) : \(\dfrac{5}{6}\)

      \(\dfrac{34}{35}\) : \(x\) = \(\dfrac{17}{5}\)                          \(\dfrac{7}{3}\) - \(x\) = \(\dfrac{66}{25}\)

      \(x\) = \(\dfrac{34}{35}\) : \(\dfrac{17}{5}\)                           \(x\) = \(\dfrac{7}{3}\) - \(\dfrac{66}{25}\)

      \(x\) = \(\dfrac{2}{7}\)                                     \(x\) = - \(\dfrac{23}{75}\)                     

a, 4/9 x ( 3/2 - 2/3 )

= 4/9 x 5/6

= 10/27 

b, 6/7 x 21/12 + 5/3

= 3/2 + 5/3

= 19/6 

c, 11/4 - 9/8 + 15/12 

= 13/8 + 15/12

= 23/8 

d, 11/10 + 3/5 : 2/3

= 11/10 + 9/10

= 2 

a) 434 - 78 - 22 + 66

= ( 434 + 66 ) - ( 78 + 22 )

= 500 - 100

= 400

400

\(\dfrac{18}{17}-\dfrac{5}{9}=\dfrac{162}{153}-\dfrac{85}{153}=\dfrac{77}{153}\)

\(\dfrac{2}{5}+\dfrac{3}{2}=\dfrac{4}{10}+\dfrac{15}{10}=\dfrac{19}{10}\)

\(\dfrac{1}{2}:\dfrac{2}{5}=\dfrac{1}{2}\times\dfrac{5}{2}=\dfrac{5}{4}\)

\(\dfrac{5}{6}\times4=\dfrac{20}{6}\)

\(\dfrac{7}{15}+\dfrac{4}{5}=\dfrac{7}{15}+\dfrac{12}{15}=\dfrac{19}{15}\)

\(\dfrac{7}{8}-\dfrac{2}{3}=\dfrac{21}{24}-\dfrac{16}{24}=\dfrac{5}{24}\)

\(\dfrac{4}{7}\times2=\dfrac{8}{7}\)

\(\dfrac{9}{5}:\dfrac{1}{6}=\dfrac{9}{5}\times6=\dfrac{54}{5}\)

a) 434 - 78 - 22 + 66

= 356 - 22 + 66

= 334 + 66

= 400

=356-22+66

=334+66

=400

\(\dfrac{3}{7}:\dfrac{2}{4}\)

\(=\dfrac{3}{7}\times\dfrac{4}{2}\)

\(=\dfrac{12}{14}\)

\(\dfrac{15}{6}:\dfrac{5}{3}\)

\(=\dfrac{15}{6}\times\dfrac{3}{5}\)

\(=\dfrac{45}{30}\)

\(\dfrac{18}{7}:\dfrac{9}{2}\)

\(=\dfrac{18}{7}\times\dfrac{2}{9}\)

\(=\dfrac{36}{63}\)

gọi số đó là ab

ab = 7 x (a+b)

10 a + b= 7a+7b

3 x a = 6 x b

vậy ab = 63