c)=13,8+(7+4,25)-5,25

=13,8+(11.25-5.25)

=13,8+6=19,8

b, = 7/9 - 2/3 - < 4/7 =3/7 > 

= 13/9 - 1

= 4/9

a)\(\frac{7}{9}-\frac{3}{7}+\frac{2}{3}-\frac{4}{7}\)

\(=\frac{7}{9}+\frac{-3}{7}+\frac{2}{3}+\frac{-4}{7}\)

\(=\left(\frac{7}{9}+\frac{2}{3}\right)+\left(\frac{-3}{7}+\frac{-4}{7}\right)\)

\(=\frac{13}{9}-1\)

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

b)13,8 + 7 - 5,25 + 4,25

=(13,8 + 7 + 4,25 ) - 5,25

=25,05 - 5,25

=19,8

a/ = (7/9+2/3)-(3/7+4/7)

    =1-1=0
 

a) 7/9 - 3/7 + 2/3 - 4/7

= 7/9 - 3/7 + 6/9 - 4/7

=( 7/9 - 6/9 ) + ( 3/7 + 4/7 )

= 1/9 + 1

=10/9

b) 13,8 + 7 - 5,25 + 4,25

=(13,8 + 7 ) - (5,25 + 4,25 )

=20,8 - 9,5

= 11,3

A,  4/9 + [3/8 + 5/8 ]

    =4/9 + 1

    =13/9

B,  [3/7+4/7]+2/3

=1+2/3

=5/3

\(a)\frac{4}{9}+\frac{3}{8}+\frac{5}{8}=\frac{4}{9}+(\frac{3}{8}+\frac{5}{8})=\frac{4}{9}+1=\frac{4+9}{9}=\frac{13}{9}\)

\(b)\frac{3}{7}+\frac{2}{3}+\frac{4}{7}=(\frac{3}{7}+\frac{4}{7})+\frac{2}{3}=1+\frac{2}{3}=\frac{3+2}{3}=\frac{5}{3}\)

\(a,\frac{4}{9}+\frac{3}{8}+\frac{5}{8}\)

\(=\left(\frac{3}{8}+\frac{5}{8}\right)+\frac{4}{9}\)

\(=1+\frac{4}{9}\)

\(=\frac{9}{9}+\frac{4}{9}=\frac{13}{9}\)

\(b,\frac{3}{7}+\frac{2}{3}+\frac{4}{7}\)

\(=\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{2}{3}\)

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

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

   \(\frac{7}{4}\times\frac{15}{7}+\frac{13}{7}\times\frac{9}{4}-\frac{2}{7}\)

\(=\left(\frac{7}{4}+\frac{9}{4}\right)\times\left(\frac{15}{7}+\frac{13}{7}\right)-\frac{2}{7}\)

\(=4\times4-\frac{2}{7}\)

\(=16-\frac{2}{7}\)

\(=\frac{112}{7}-\frac{2}{7}\)

\(=\frac{110}{7}\)

25/9

3/10

\(a,\dfrac{47}{3}:3-\dfrac{37}{3}:3+\dfrac{5}{3}=\dfrac{1}{3}\times\left(\dfrac{47}{3}-\dfrac{37}{3}\right)+\dfrac{5}{3}=\dfrac{10}{9}+\dfrac{5}{3}=\dfrac{10}{9}+\dfrac{15}{9}=\dfrac{25}{9}\)

\(b,\dfrac{3}{5}:\dfrac{7}{9}\times\dfrac{7}{9}:2=\dfrac{27}{35}\times\dfrac{7}{18}=\dfrac{3}{10}\)