Question

1.Tìm x, biết:

a) 7/8 + x = 4/7 b) 6 – x = (-3)/4 c) 1/(-5) + x = 3/4 d) –6 – x = (-3)/5

e) - 2/6 + x = 5/7 f) -8 – x = (-5)/3 g) - 2/10 – x = - 9/8 h) 8 – x = (-1)/6

i) - 2/5 + x = 5/7 j) -2 – x = (-5)/3 k) - 1/6 – x = - 9/8 l) 8 – x = (-1)/5

2. Tính:

a) -7/3 + 4/9 b) -8/18 - 15/56 c) (-7) - (-3/4) d) 0,15 + (-5/12)

e) -1/42 + -1/28 f) -1/21 + -1/36 g) 5,5 - (-2/7) h) 0,9 - (-4/7)

Answer 1

Bài 1:

a; \(\dfrac{7}{8}\) + \(x\) = \(\dfrac{4}{7}\)

     \(x\) = \(\dfrac{4}{7}\) - \(\dfrac{7}{8}\)

     \(x\) = \(\dfrac{32}{56}\) - \(\dfrac{49}{56}\)

     \(x=-\) \(\dfrac{49}{56}\)

Vậy \(x=-\dfrac{49}{56}\)

b; 6 - \(x\) = - \(\dfrac{3}{4}\)

         \(x\) = 6 + \(\dfrac{3}{4}\)

         \(x\) = \(\dfrac{24}{4}+\dfrac{3}{4}\)

         \(x=\dfrac{27}{4}\)

Vậy \(x=\dfrac{27}{4}\) 

c; \(\dfrac{1}{-5}\) + \(x\) = \(\dfrac{3}{4}\)

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

              \(x=\dfrac{15}{20}\) + \(\dfrac{4}{20}\)

               \(x=\dfrac{19}{20}\)

Vậy \(x=\dfrac{19}{20}\) 

Answer 2

      Bài 1:

d; - 6 - \(x\) = - \(\dfrac{3}{5}\)

      \(x\)   = - 6 + \(\dfrac{3}{5}\)

       \(x=-\dfrac{30}{5}\) + \(\dfrac{3}{5}\)

       \(x=-\dfrac{27}{5}\)

Vậy \(x=-\dfrac{27}{5}\)

e; - \(\dfrac{2}{6}\) + \(x\) = \(\dfrac{5}{7}\)

             \(x\) = \(\dfrac{5}{7}\) + \(\dfrac{2}{6}\)

             \(x\) = \(\dfrac{15}{21}\) + \(\dfrac{1}{3}\)

              \(x=\dfrac{15}{21}\) + \(\dfrac{7}{21}\)

               \(x=\dfrac{22}{21}\)

Vậy \(x=\dfrac{22}{21}\) 

f; - 8 - \(x\) =  - \(\dfrac{5}{3}\)

          \(x\) = \(-\dfrac{5}{3}\) + 8

         \(x\) = \(\dfrac{-5}{3}\) + \(\dfrac{24}{3}\)

         \(x\) = \(\dfrac{-19}{3}\)

Vậy \(x=-\dfrac{19}{3}\) 

 

            

 

Answer 3

Bài 1g; - \(\dfrac{2}{10}\) - \(x\) = - \(\dfrac{9}{8}\)

                \(x\) = - \(\dfrac{2}{10}\) + \(\dfrac{9}{8}\)

                \(x\) = - \(\dfrac{8}{40}\) + \(\dfrac{45}{40}\)

                 \(x\) = \(\dfrac{37}{40}\) 

               Vậy \(x=\dfrac{37}{40}\)

h; 8 - \(x\) = \(-\dfrac{1}{6}\)

           \(x\) = 8 + \(\dfrac{1}{6}\)

          \(x\) = \(\dfrac{48}{6}\) + \(\dfrac{1}{6}\)

          \(x=\dfrac{49}{6}\)

Vậy \(x=\dfrac{49}{6}\)

i; - \(\dfrac{2}{5}\) + \(x\) = \(\dfrac{5}{7}\)

          \(x\) = \(\dfrac{5}{7}\) + \(\dfrac{2}{5}\)

          \(x\) = \(\dfrac{39}{35}\) 

Vậy \(x=\dfrac{39}{35}\)

 

Answer 4

j; - 2 - \(x\) = - \(\dfrac{5}{3}\)

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

          \(x\) = - \(\dfrac{6}{3}\) + \(\dfrac{5}{3}\)

         \(x\) = - \(\dfrac{1}{3}\)

Vậy \(x=-\dfrac{1}{3}\)

k; - \(\dfrac{1}{6}\) - \(x\) = -\(\dfrac{9}{8}\)

           \(x\) = - \(\dfrac{1}{6}\) + \(\dfrac{9}{8}\)

            \(x\) = - \(\dfrac{4}{24}\) + \(\dfrac{27}{24}\)

            \(x=\dfrac{23}{24}\)

Vậy \(x=\dfrac{23}{24}\)

l; 8 - \(x\) = - \(\dfrac{1}{5}\)

       \(x\) = 8 + \(\dfrac{1}{5}\)

       \(x\) = \(\dfrac{40}{5}\) + \(\dfrac{1}{5}\)

        \(x=\dfrac{41}{5}\)

Vậy \(x=\dfrac{41}{5}\) 

Answer 5

Bài 2:

a; - \(\dfrac{7}{3}\) + \(\dfrac{4}{9}\)

  = \(-\dfrac{21}{9}\) + \(\dfrac{4}{9}\)

 = \(\dfrac{-17}{9}\)

b; - \(\dfrac{8}{18}\) - \(\dfrac{15}{56}\)

=  \(\dfrac{-224}{504}\) - \(\dfrac{135}{504}\)

= - \(\dfrac{359}{504}\)

 

Answer 6

c; (-7) - (- \(\dfrac{3}{4}\)) 

= - 7 + \(\dfrac{3}{4}\)

= - \(\dfrac{28}{4}\) + \(\dfrac{3}{4}\)

= - \(\dfrac{25}{4}\) 

Answer 7

d; 0,15 + (- \(\dfrac{5}{12}\))

 = \(\dfrac{3}{20}\) - \(\dfrac{5}{12}\)

= \(\dfrac{9}{60}\) - \(\dfrac{25}{60}\)

= - \(\dfrac{4}{15}\) 

e; - \(\dfrac{1}{42}\) + - \(\dfrac{1}{28}\)

=  - \(\dfrac{2}{84}\) - \(\dfrac{3}{84}\)

= - \(\dfrac{5}{84}\) 

Answer 8

f; - \(\dfrac{1}{21}\) - \(\dfrac{1}{36}\)

= - \(\dfrac{12}{252}\) - \(\dfrac{7}{252}\)

= - \(\dfrac{19}{252}\) 

g; 5,5 - (- \(\dfrac{2}{7}\))

= \(\dfrac{11}{2}\) + \(\dfrac{2}{7}\)

= \(\dfrac{77}{14}\) + \(\dfrac{4}{14}\)

= \(\dfrac{81}{14}\)

 

Answer 9

h; 0,9 - (- \(\dfrac{4}{7}\))

 = \(\dfrac{9}{10}\) + \(\dfrac{4}{7}\)

 = \(\dfrac{63}{70}\) + \(\dfrac{40}{70}\) 

= \(\dfrac{103}{70}\)